Your search found 68 records
1 Ashraf, M.; Bhatti, Muhammad Tousif; Shakir, A. S. 2016. River bank erosion and channel evolution in sand-bed braided reach of River Chenab: role of floods during different flow regimes. Arabian Journal of Geosciences, 9(2):1-10. [doi: https://doi.org/10.1007/s12517-015-2114-y]
Riverbank protection ; Erosion control ; Flooding ; Landsat ; Imagery ; Sand ; Open channels ; Monsoon climate ; Flow discharge ; Stream flow ; Environmental protection / Pakistan / Chenab River
(Location: IWMI HQ Call no: e-copy only Record No: H047488)
(5.03 MB)
Braided reaches of large rivers in alluvial plains show major morphological changes, particularly the external bank erosion, due to the flood events. This paper highlights the bank erosion and channel evolution induced by eleven different flood events in a 7-km long reach of the River Chenab, Pakistan. The impact of floods on river bank erosion and channel evolution is analyzed under low and high flow conditions. Flood-induced changes, for river’s external banks and channel evolution, were assessed by processing Landsat ETM+ images in ArcGIS tool, and their inter-relationship is evaluated through regression analysis. The results revealed that the major morphological changes were triggered by the flood events occurred during the high flow or Monsoon season (July–September), whereas the flood events of similar magnitude occurring during low flow season (October–March) did not induce such changes. Mostly, the erosion remained limited to the middle part of the reach,where the branch channel flows along the bank. The average annual bank erosion rates are much higher as compared with a global scale. Data analysis showed a strong correlation between the mean high flows and total bank erosion indicating that Monsoon seasonal flows and floods are responsible for bank erosion. The present study further identifies the river bank locations highly susceptible to erosion by developing the correlation between bank erosion and branch channel progression. Strong correlation for bank erosion could be established with the shift of branch channels position flowing along the banks in braided reaches of sand bed rivers. However, the presence of sand bars along the river banks resulted in reduced erosion that weakens this relationship. The findings of the present study can help develop better understanding about the bank erosion process and constitute a key element to inform and improve river bank management.
2 Pekel, J.-F.; Cottam, A.; Gorelick, N.; Belward, A. S. 2016. High-resolution mapping of global surface water and its long-term changes. Nature, 540(7633):418-422. [doi: https://doi.org/10.1038/nature20584]
Surface water ; Mapping ; Satellite imagery ; Landsat ; Earth observation satellites ; Water distribution ; Geographical distribution ; Seasonal variation ; Expert systems ; Climate change ; Hydrology ; Models ; Drought ; Evaporation ; Human behavior ; Lakes ; Plateaus / Central Asia / USA / Australia / Aral Sea / Tibetan plateau
(Location: IWMI HQ Call no: e-copy only Record No: H047905)
(8.75 MB)
The location and persistence of surface water (inland and coastal) is both affected by climate and human activity1 and affects climate2,3 , biological diversity4 and human wellbeing5,6 . Global data sets documenting surface water location and seasonality have been produced from inventories and national descriptions7 , statistical extrapolation of regional data8 and satellite imagery9–12, but measuring long-term changes at high resolution remains a challenge. Here, using three million Landsat satellite images13, we quantify changes in global surface water over the past 32 years at 30-metre resolution. We record the months and years when water was present, where occurrence changed and what form changes took in terms of seasonality and persistence. Between 1984 and 2015 permanent surface water has disappeared from an area of almost 90,000 square kilometres, roughly equivalent to that of Lake Superior, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. All continental regions show a net increase in permanent water, except Oceania, which has a fractional (one per cent) net loss. Much of the increase is from reservoir filling, although climate change14 is also implicated. Loss is more geographically concentrated than gain. Over 70 per cent of global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions including river diversion or damming and unregulated withdrawal15,16. Losses in Australia17 and the USA18 linked to long-term droughts are also evident. This globally consistent, validated data set shows that impacts of climate change and climate oscillations on surface water occurrence can be measured and that evidence can be gathered to show how surface water is altered by human activities. We anticipate that this freely available data will improve the modelling of surface forcing, provide evidence of state and change in wetland ecotones (the transition areas between biomes), and inform water-management decision-making.
3 Tadesse, L.; Suryabhagavan, K. V.; Sridhar, G.; Legesse, G. 2017. Land use and land cover changes and soil erosion in Yezat Watershed, North western Ethiopia. International Soil and Water Conservation Research, 5(2):85-94. [doi: https://doi.org/10.1016/j.iswcr.2017.05.004]
Land use ; Land cover change ; Watersheds ; Soil erosion models ; GIS ; Remote sensing ; Satellite imagery ; Landsat ; Vegetation ; Grasslands ; Farmland ; Woodlands ; Shrubs ; Biomass ; Spatial distribution / Ethiopia / Yezat Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H048161)
http://www.sciencedirect.com/science/article/pii/S2095633916301393/pdfft?md5=db1a36ec40258ace455dc8bd1f7f2b25&pid=1-s2.0-S2095633916301393-main.pdf
https://vlibrary.iwmi.org/pdf/H048161.pdf
https://vlibrary.iwmi.org/pdf/H048161.pdf
(4.19 MB) (4.19 MB)
Soil erosion affects land qualities and water resources. This problem is severe in Ethiopia due to its topographic features. The present research was aimed to estimate spatiotemporal changes in land-use/land-cover pattern and soil erosion in the Yezat watershed in Ethiopia. This study was carried out by using landsat imageries of 2001, 2010 and 2015. Images were classified into categories using supervised classification by maximum likelihood algorithm. They were also classified into different biomass levels by using Normalized Difference Vegetation Index (NDVI) analysis. Revised Universal Soil Loss Equation modeling was applied in a GIS environment to quantify the potential soil erosion risk. The area under grassland, woodland and homesteads have increased by 610.69 (4%), 101.69 (0.67%) and 126.6 ha (0.83%) during 2001–2015. The extent of cultivated land and shrub/bushland was reduced by 323.43(0.02%) and 515.44 ha (3.41%), respectively, during the same period. The vegetation cover in the watershed decreased by 91% during 2001–2010, and increased by 88% during 2010–2015. Increase of NDVI values indicates better ground cover due to implementation of integrated watershed development program in the region. The estimated annual soil losses were 7.2 t ha-1 yr-1 in 2001, 7.7 t ha-1 yr-1 in 2010 and 4.8 t ha-1 yr-1 in 2015. Management interventions are necessary to improve the status and utilization of watershed resources in response to sustainable land management practices for sustainable livelihood of the local people.
4 Talukdar, S.; Pal, S. 2017. Impact of dam on inundation regime of flood plain wetland of Punarbhaba River Basin of barind tract of Indo-Bangladesh. International Soil and Water Conservation Research, 5(2):109-121. [doi: https://doi.org/10.1016/j.iswcr.2017.05.003]
Floodplains ; Wetlands ; Dams ; Flooding ; Water levels ; Water availability ; River basins ; Flow discharge ; Hydrological regime ; Monsoon climate ; Rain ; Satellite imagery ; Landsat ; Ecological factors ; Seasonal variation / India / Bangladesh / Punarbhaba River Basin
(Location: IWMI HQ Call no: e-copy only Record No: H048163)
http://www.sciencedirect.com/science/article/pii/S2095633917300254/pdfft?md5=584dcd662bb7c4d0a6900bc2cfae0a29&pid=1-s2.0-S2095633917300254-main.pdf
https://vlibrary.iwmi.org/pdf/H048163.pdf
https://vlibrary.iwmi.org/pdf/H048163.pdf
(4.02 MB) (4.02 MB)
Present study raises a serious issue of wetland loss and transformation due to damming and water diversion. At present study, it is noticed that overall rainfall trend (-0.006) of the study period (1978–2015) remains unchanged but riparian wetland area is attenuated after damming both pre monsoon (March to May) and post monsoon season (October to December). Total wetland area in pre- and postmonsoon seasons is respectively reduced from 42.2 km2 to 27.87 km2 , and from 277.85 km2 to 220.90 km2 in post dam period. Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river. Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice. This extreme issue will invite instability in socio-ecological setup of the neighbouring region.
5 Dinka, M. O. 2017. Lake Basaka expansion: challenges for the sustainability of the Matahara Irrigation Scheme, Awash River Basin (Ethiopia). Irrigation and Drainage, 66(3):305-315. [doi: https://doi.org/10.1002/ird.2114]
Lakes ; Expansion ; Groundwater table ; Water quality ; Salinity ; Waterlogging ; Irrigation schemes ; Sustainability ; Landsat ; Imagery ; Spatial distribution ; Mapping ; Soil quality ; Soil fertility ; Agricultural production ; Sugarcane ; Plantations ; Productivity / Ethiopia / Lake Basaka / Awash River Basin / Matahara Irrigation Scheme
(Location: IWMI HQ Call no: e-copy only Record No: H048188)
(0.91 MB)
The Matahara Sugar Estate (MSE), after nearly 60 years of irrigation, is experiencing the effects of waterlogging and salinization in some fields. The problem is believed to be the result of the expansion of (saline and alkaline) Lake Basaka towards the plantation fields. The objective of this study was to determine the geometry of the lake (area and shape) in roughly the past half- century (1957–2015) from both Landsat images and local information and then assess its negative effects on MSE’s soil and water quality. Monthly groundwater (GW) depth was monitored using piezometer tubes. Water and soil samples were collected from each of the piezometer locations and analysed for important physico-chemical parameters. The results indicate that the lake expanded approximately 47.3 km2 in the past half-century. The soil quality was found to be very poor in plantation sections with very shallow GW depth and severe salinity conditions. The lake, as revealed by the results, is intruding into the groundwater system of MSE on the Abadir side. Assuming continuation of the past trends, the lake is expected to inundate parts of MSE in the next few years and, hence, challenge the production and productivity of MSE significantly. The lake has the potential to join the Awash River, thereby impacting all downstream irrigation developments in the basin and the livelihood of the people depending on the water resources. As the area is situated in the uppermost part of Main Ethiopian Rift Valley, other factors are expected to exacerbate its expansion even in the future. Overall, the study results present the potential damage caused by the lake to MSE and provides valuable information for the reclamation measures to be taken for the sustainability of MSE.
6 Zimba, H.; Kawawa, B.; Chabala, A.; Phiri, W.; Selsam, P.; Meinhardt, M.; Nyambe, I. 2018. Assessment of trends in inundation extent in the Barotse Floodplain, upper Zambezi River Basin: a remote sensing-based approach. Journal of Hydrology: Regional Studies, 15:149-170. [doi: https://doi.org/10.1016/j.ejrh.2018.01.002]
Flooding ; River basins ; Floodplains ; Discharges ; Assessment ; Remote sensing ; Water levels ; Satellite imagery ; Landsat ; Wetlands ; Rain ; Time series analysis / Zambia / Zambezi River Basin / Barotse Floodplain
(Location: IWMI HQ Call no: e-copy only Record No: H048535)
https://www.sciencedirect.com/science/article/pii/S2214581817300575/pdfft?md5=5c58dd751d58befa140e668ce9df8cea&pid=1-s2.0-S2214581817300575-main.pdf
https://vlibrary.iwmi.org/pdf/H048535.pdf
https://vlibrary.iwmi.org/pdf/H048535.pdf
(3.08 MB) (3.08 MB)
Study region: The annually flooded Barotse Floodplain in the upper Zambezi River Basin in the Western Province of Zambia, Southern Africa.
Study focus: Discharge variability plays a significant role in inundation extent and thus it controls habitat conditions of river channels and the linked wetlands. The linkage between discharge and inundation extent in the Barotse Floodplain allowed us to analyse the trends in extent overtime using optical satellite imagery MODIS. The Desert Flood Index, a surface water extraction algorithm, was used to generate time series of inundation extent. For validation of the inundation extent we used a flood mask extracted from a supervised classification land cover map using Landsat imagery. The land cover map was validated using the error matrix method with ground truthed data. The estimated inundation extent time series enabled us to test the inundation correlation with discharge and water level using Pearson r correlation, a parametric statistical test. Based on the established correlation we used the Mann–Kendall, a non-parametric test, to analyse trends in the inundation extent and discharge and water level time series from which we made inferences on the direction of the historical trend in inundation extent.
New hydrological insights for the region: The results revealed that there is observable inter-annual variability in inundation extent in the Barotse Floodplain with prominent differences demonstrated in both the flood ascending/peak and receding period. For the period 2003–2013 the results indicated a rising trend in inundation extent with a Mann–Kendall Z statistic of 1.71 and increase in magnitude of 33.1 km2 at significance level alpha of 0.05. Strong correlations between inundation extent and water level and between inundation extent and discharge with correlation coefficients of determination of 0.86 and 0.89 respectively were observed. For the period 2000–2011 water level time series showed a rising trend with the Mann–Kendall Z statistic of 2.97 and increase in magnitude of 0.1 m at significance level alpha of 0.05. Overall, during the period 1952–2004 discharge in the floodplain showed a declining trend with Mann–Kendall Z statistics of -2.88 and -3.38 at the inlet and outlet of the floodplain respectively. By correlation inference, the overall inundation extent trend in the floodplain was in a downward movement. Rainfall and discharge variability, high evapotranspiration and the changes in the land cover-use in the catchment of the floodplain are largely the factors affecting the observed variability and trends in inundation extent in the floodplain. The presented remote sensing based approach significantly reduces the need for the expensive and time limiting traditional physical field based wetland inundation mapping methods that form a limitation for achieving progress in wetland monitoring especially in open and sparsely gauged floodplains such as the Barotse.
Study focus: Discharge variability plays a significant role in inundation extent and thus it controls habitat conditions of river channels and the linked wetlands. The linkage between discharge and inundation extent in the Barotse Floodplain allowed us to analyse the trends in extent overtime using optical satellite imagery MODIS. The Desert Flood Index, a surface water extraction algorithm, was used to generate time series of inundation extent. For validation of the inundation extent we used a flood mask extracted from a supervised classification land cover map using Landsat imagery. The land cover map was validated using the error matrix method with ground truthed data. The estimated inundation extent time series enabled us to test the inundation correlation with discharge and water level using Pearson r correlation, a parametric statistical test. Based on the established correlation we used the Mann–Kendall, a non-parametric test, to analyse trends in the inundation extent and discharge and water level time series from which we made inferences on the direction of the historical trend in inundation extent.
New hydrological insights for the region: The results revealed that there is observable inter-annual variability in inundation extent in the Barotse Floodplain with prominent differences demonstrated in both the flood ascending/peak and receding period. For the period 2003–2013 the results indicated a rising trend in inundation extent with a Mann–Kendall Z statistic of 1.71 and increase in magnitude of 33.1 km2 at significance level alpha of 0.05. Strong correlations between inundation extent and water level and between inundation extent and discharge with correlation coefficients of determination of 0.86 and 0.89 respectively were observed. For the period 2000–2011 water level time series showed a rising trend with the Mann–Kendall Z statistic of 2.97 and increase in magnitude of 0.1 m at significance level alpha of 0.05. Overall, during the period 1952–2004 discharge in the floodplain showed a declining trend with Mann–Kendall Z statistics of -2.88 and -3.38 at the inlet and outlet of the floodplain respectively. By correlation inference, the overall inundation extent trend in the floodplain was in a downward movement. Rainfall and discharge variability, high evapotranspiration and the changes in the land cover-use in the catchment of the floodplain are largely the factors affecting the observed variability and trends in inundation extent in the floodplain. The presented remote sensing based approach significantly reduces the need for the expensive and time limiting traditional physical field based wetland inundation mapping methods that form a limitation for achieving progress in wetland monitoring especially in open and sparsely gauged floodplains such as the Barotse.
7 Nhamo, Luxon; van Dijk, R.; Magidi, J.; Wiberg, David; Tshikolomo, K. 2018. Improving the accuracy of remotely sensed irrigated areas using post-classification enhancement through UAV [Unmanned Aerial Vehicle] capability. Remote Sensing, 10(5):1-12. (Special issue: Remote Sensing for Crop Water Management). [doi: https://doi.org/10.3390/rs10050712]
Irrigated sites ; Remote sensing ; Unmanned aerial vehicles ; Land use mapping ; Land cover mapping ; Satellite imagery ; Landsat ; Farmland ; Vegetation index ; Crops / South Africa / Limpopo Province / Venda / Gazankulu
(Location: IWMI HQ Call no: e-copy only Record No: H048752)
(2.23 MB) (2.23 MB)
Although advances in remote sensing have enhanced mapping and monitoring of irrigated areas, producing accurate cropping information through satellite image classification remains elusive due to the complexity of landscapes, changes in reflectance of different land-covers, the remote sensing data selected, and image processing methods used, among others. This study extracted agricultural fields in the former homelands of Venda and Gazankulu in Limpopo Province, South Africa. Landsat 8 imageries for 2015 were used, applying the maximum likelihood supervised classifier to delineate the agricultural fields. The normalized difference vegetation index (NDVI) applied on Landsat imageries on the mapped fields during the dry season (July to August) was used to identify irrigated areas, because years of satellite data analysis suggest that healthy crop conditions during dry seasons are only possible with irrigation. Ground truth points totaling 137 were collected during fieldwork for pre-processing and accuracy assessment. An accuracy of 96% was achieved on the mapped agricultural fields, yet the irrigated area map produced an initial accuracy of only 71%. This study explains and improves the 29% error margin from the irrigated areas. Accuracy was enhanced through post-classification correction (PCC) using 74 post-classification points randomly selected from the 2015 irrigated area map. High resolution aerial photographs of the 74 sample fields were acquired by an unmanned aerial vehicle (UAV) to give a clearer picture of the irrigated fields. The analysis shows that mapped irrigated fields that presented anomalies included abandoned croplands that had green invasive alien species or abandoned fruit plantations that had high NDVI values. The PCC analysis improved irrigated area mapping accuracy from 71% to 95%.
8 Korah, P. I.; Nunbogu, A. M.; Akanbang, B. A. A. 2018. Spatio-temporal dynamics and livelihoods transformation in Wa, Ghana. Land Use Policy, 77:174-185. [doi: https://doi.org/10.1016/j.landusepol.2018.05.039]
Living standards ; Sustainability ; Urbanization ; Spatial planning ; Land use ; Land cover ; Satellite imagery ; Landsat ; Strategies ; Municipal governments ; Households ; Socioeconomic environment ; Periurban areas / Ghana / Wa Municipality
(Location: IWMI HQ Call no: e-copy only Record No: H048918)
(2.24 MB)
This paper examines how indigenous peri-urban households in Wa, one of the fastest growing towns in Ghana are adapting to the effects of physical transformation of their environment. By analysing Landsat satellite images and using social research methods, the paper discusses the nature and extent of urban growth, its impact on periurban livelihoods, and the coping strategies of peri-urban households. Findings show that urban land in Wa increased by 5.73 times—from 5.75 km2 in 1986 to 32.93 km2 in 2016 with an annual growth rate of 5.9%. This growth led to the conversion of agricultural lands into residential and other uses. As a result, many indigenous peri-urban households are abandoning agriculture in search for urban-based employment as a safety net. The study recommends partnership between local government and landowners to identify and protect high potential agricultural lands in Wa; modernisation of the land governance and management processes in view of the loss of cultural and spiritual values associated with land; prioritisation of physical and spatial planning at the district level; and equipping indigenous peri-urban households with skills to assist them create sustainable livelihoods to compensate for the loss of their agriculture lands.
9 Moges, M. A.; Schmitter, Petra; Tilahun, S. A.; Ayana, E. K.; Ketema, A. A.; Nigussie, T. E.; Steenhuis, T. S. 2017. Water Quality Assessment by Measuring and Using Landsat 7 ETM+ Images for the Current and Previous Trend Perspective: Lake Tana Ethiopia. Water Research, 9:1564-1585. [doi: https://doi.org/10.4236/jwarp.2017.912099]
Water quality ; Assessment ; Landsat ; Deltas ; Lakes ; Sediment ; Nutrients ; Watersheds ; Water conservation ; Soil conservation ; River basins ; Phosphorus ; Remote sensing / Ethiopia / Lake Tana
(Location: IWMI HQ Call no: e-copy only Record No: H048966)
https://www.scirp.org/journal/PaperDownload.aspx?paperID=80775
https://vlibrary.iwmi.org/pdf/H048966.pdf
https://vlibrary.iwmi.org/pdf/H048966.pdf
(3.89 MB)
Recently there are signs of water quality impairment in Lake Tana, the largest fresh water in Ethiopia. The lake is the growth corridor of the government and supports millions of livelihood around. In order to sustain the benefit and maintain the ecosystem of the lake, the lake health has to be kept safe. Therefore monitoring and evaluation of the water quality of lake is very vital. This study focuses on current and previous trends water quality of the lake through measurements and Landsat Images near entry of Gumera River. Statistical analysis of the physical (Turbidity and STD and biological (Cha-a,) and chemical (DPC) water quality parameters were done. Linear and non-linear regression models between water quality parameter and reflectance of Landsat 7 ETM+ images were fitted based on band combinations. Pervious trend in turbidity was analyzed based on the regression models. The results showed that reflectance and turbidity satisfactorily result with an R2 ranging from 0.61 - 0.68. Form 1999-2014 the turbidity of the lake has indicated an increasing trend. Delta development near the entry of Gumera River has been enlarged by 48% because of an increase sediment inflow. The sign in the decreasing water quality of the lake was attributed to the non-point source sediment and nutrient inflow to the lake with high erosion rate from the watersheds. Measures to reduce the non-point source sediment and nutrient inflow by targeting the source areas (hot spots) in the agricultural watersheds need to be priority for stakeholders working on the soil and water conservation. Moreover, reducing the recession agriculture around the lake and wetland management could be crucial for improving lake water quality.
10 Tarpanelli, A.; Santi, E.; Tourian, M. J.; Filippucci, P.; Amarnath, Giriraj; Brocca, L. 2019. Daily river discharge estimates by merging satellite optical sensors and radar altimetry through artificial neural network. IEEE Transactions on Geoscience and Remote Sensing, 57(1):329-341. [doi: https://doi.org/10.1109/TGRS.2018.2854625]
Rivers ; Discharges ; Estimation ; Water levels ; Remote sensing ; Satellite imagery ; Landsat ; Moderate Resolution Imaging Spectroradiometer ; Neural networks ; Radar ; Performance indexes ; Time series analysis ; Case studies / Nigeria / Italy / Niger River / Benue River / Po River / Lokoja / Pontelagoscuro
(Location: IWMI HQ Call no: e-copy only Record No: H048997)
(2.81 MB)
Thanks to the large number of satellites, the multimission approach is becoming a viable method to integrate measurements and intensify the number of samples in space and time for monitoring the earth system. In this paper, we merged data from different satellite missions, optical sensors, and altimetry, for estimating daily river discharge through the application of the artificial neural network (ANN) technique. ANN was selected among other retrieval techniques because it offers an easy but effective way of combining input data from different sources into the same retrieval algorithm. The network is trained in a calibration period and validated in an independent period against in situ observations of river discharge for two gauging sites: Lokoja along the Niger River and Pontelagoscuro along the Po River. For optical sensors, we found that the temporal resolution is more important than the spatial resolution for obtaining accurate discharge estimates. Our results show that Landsat fails in the estimation of extreme events by missing most of the peak values due to its long revisit time (14–16 days). Better performances are obtained from Moderate Resolution Imaging Spectroradiometer (MODIS) and Medium Resolution Imaging Spectrometer. Radar altimetry provides results in between MODIS-TERRA and MODIS-AQUA at Lokoja, whereas it outperforms all single optical sensors at Pontelagoscuro. The multimission approach, involving optical sensors and altimetry, is found the most reliable tool to estimate river discharge with a relative root-mean-square error of 0.12% and 0.27% and Nash-Sutcliffe coefficient of 0.98 and 0.83 for the Niger and Po rivers, respectively.
11 Bunting, P.; Rosenqvist, A.; Lucas, R. M.; Rebelo, Lisa-Maria; Thomas, N.; Hardy, A.; Itoh, T.; Shimada, M.; Finlayson, C. M. 2018. The global mangrove watch - a New 2010 global baseline of mangrove extent. Remote Sensing, 10(10):1-19. [doi: https://doi.org/10.3390/rs10101669]
Mangroves ; Wetlands ; Mapping ; Landsat ; Satellite imagery ; Satellite observation ; Earth observation satellites ; Human behaviour ; Coastal area ; Deltas ; Environmental monitoring
(Location: IWMI HQ Call no: e-copy only Record No: H049127)
(18 MB)
This study presents a new global baseline of mangrove extent for 2010 and has been released as the first output of the Global Mangrove Watch (GMW) initiative. This is the first study to apply a globally consistent and automated method for mapping mangroves, identifying a global extent of 137,600 km 2 . The overall accuracy for mangrove extent was 94.0% with a 99% likelihood that the true value is between 93.6–94.5%, using 53,878 accuracy points across 20 sites distributed globally. Using the geographic regions of the Ramsar Convention on Wetlands, Asia has the highest proportion of mangroves with 38.7% of the global total, while Latin America and the Caribbean have 20.3%, Africa has 20.0%, Oceania has 11.9%, North America has 8.4% and the European Overseas Territories have 0.7%. The methodology developed is primarily based on the classification of ALOS PALSAR and Landsat sensor data, where a habitat mask was first generated, within which the classification of mangrove was undertaken using the Extremely Randomized Trees classifier. This new globally consistent baseline will also form the basis of a mangrove monitoring system using JAXA JERS-1 SAR, ALOS PALSAR and ALOS-2 PALSAR-2 radar data to assess mangrove change from 1996 to the present. However, when using the product, users should note that a minimum mapping unit of 1 ha is recommended and that the error increases in regions of disturbance and where narrow strips or smaller fragmented areas of mangroves are present. Artefacts due to cloud cover and the Landsat-7 SLC-off error are also present in some areas, particularly regions of West Africa due to the lack of Landsat-5 data and persistence cloud cover. In the future, consideration will be given to the production of a new global baseline based on 10 m Sentinel-2 composites.
12 Elnmer, A.; Khadr, M.; Kanae, S.; Tawfik, A. 2019. Mapping daily and seasonally evapotranspiration using remote sensing techniques over the Nile Delta. Agricultural Water Management, 213:682-692. [doi: https://doi.org/10.1016/j.agwat.2018.11.009]
Remote sensing ; Evapotranspiration ; Mapping ; Techniques ; Water balance ; Water use ; Water requirements ; Water supply ; Landsat ; Satellite imagery ; Irrigation efficiency ; Precipitation ; Assessment / Egypt / Nile Delta
(Location: IWMI HQ Call no: e-copy only Record No: H049131)
(8.56 MB)
The rapid escalation in water demands for agriculture, domestic, and industry sectors requires skillful management of this limited resource. Globally, the agriculture sector is considered the main user of the water resource. Actual evapotranspiration (ETc) is an important tool in determining the water requirements of different crops. Therefore, precise estimation of the ETc is the major parameter in the water balance of arid and semi-arid agriculture regions such as Egypt. Recently, both Remote Sensing and Geographical Information Systems (GIS) become the main techniques that can be efficiently used for estimating the ETc on regional and global coverage. The main goal of this study was to estimate the daily and seasonally ETc over the Nile delta using remote sensing techniques. These techniques were Surface Energy Balance for Land (SEBAL) algorithm with 24 Landsat 8 images. Additionally, FAO-Penman-Monteith method was used to validate the derived ETc from SEBAL algorithm under the same conditions using several performance criteria to assess the performance of the SEBAL algorithm with Landsat 8 in estimating the ETc over the Nile delta. The results revealed that the SEBAL algorithm with Landsat 8 images appears to provide an acceptable estimation of the spatial and temporal distributions of ETc over the Nile delta with acceptable accuracy with R2 = 97.83%, RMSE about 0.469 mm/day and 15.9% NRMSE. The derived ETc from SEBAL algorithm was then used to estimate the water balance and the irrigation efficiency of the study area. Results of water balance estimates revealed that most of the seasonal ETc (93%) was originally met by surface water and groundwater supplies; however, the remaining portion (7%) was particularly met by precipitation. Furthermore, the estimated irrigation efficiency was about 48.6% in the central portion of the Nile delta. Overall, the performance of the derived ETc from SEBAL algorithm compared to available ground datasets demonstrates the potential of using the SEBAL algorithm with Landsat 8 images for water use and water balance estimates within the Nile delta.
13 Ghale, Y. A. G.; Baykara, M.; Unal, A. 2019. Investigating the interaction between agricultural lands and Urmia Lake ecosystem using remote sensing techniques and hydro-climatic data analysis. Agricultural Water Management, 221:566-579. [doi: https://doi.org/10.1016/j.agwat.2019.05.028]
Farmland ; Lakes ; Ecosystems ; Agricultural development ; Water management ; Hydroclimatology ; Remote sensing ; Techniques ; Landsat ; Satellite imagery ; Soil salinity ; Desertification ; Land cover change ; Irrigated land ; Anthropogenic factors ; Climatic factors / Iran / Urmia Lake
(Location: IWMI HQ Call no: e-copy only Record No: H049260)
(6.51 MB)
Urmia Lake (UL) located in the northwest of Iran, is one of the largest hypersaline lakes in the world. In recent years, most of the lake has been rendered to unusable lands. Drought and rapid increase in agricultural activities are the most important reasons behind the shrinkage of the lake. In this study, hydro-climatic data, Landsat satellite images and image processing techniques were used to detect the spatio-temporal land cover changes and salinization progress in Urmia Lake Basin (ULB) between 1975 and 2019. Increasing the area of irrigated lands from 1265 km2 in 1975 to 5525 km2 in 2011 in contrast to decreasing the water surface area of UL from 5982 km2 in 1995 to 586 km2 in 2014 and extension of salinization in the basin are the most important and thoughtful results of this study. Even the agricultural lands in the regions close to the lake have been affected by this environmental problem. The climatic conditions have gradually improved after 2014 and the government has released more water from dams to the lake. On the other hand, the area of irrigated lands has gradually decreased by 12% in the same period. As a result of these positive changes, the water surface area of the lake has gradually increased over 1000 km2. Based on the results of this study, both anthropogenic and climatic factors have played a positive role in UL restoration. Improvement of agricultural methods and providing a sustainable agricultural water management system under a changing climate can play the most effective role in the lake rehabilitation.
14 Higley, M. C.; Conroy, J. L. 2019. The hydrological response of surface water to recent climate variability: a remote sensing case study from the central tropical Pacific. Hydrological Processes, 33(16):2227-2239. [doi: https://doi.org/10.1002/hyp.13465]
Surface water ; Climate change ; Hydrological factors ; Remote sensing ; Case studies ; Freshwater ; Groundwater ; Evaporation ; El Nino-Southern Oscillation ; Satellite imagery ; Landsat ; Normalized difference vegetation index ; Islands / Pacific Islands / Kiribati / Kiritimati
(Location: IWMI HQ Call no: e-copy only Record No: H049284)
(2.56 MB)
For small tropical islands with limited freshwater resources, understanding how island hydrology is influenced by regional climate is important, considering projected hydroclimate and sea level changes as well as growing populations dependent on limited groundwater resources. However, the relationship between climate variability and hydrologic variability for many tropical islands remains uncertain due to local hydroclimatic data scarcity. Here, we present a case study from Kiritimati, Republic of Kiribati (2°N, 157°W), utilizing the normalized difference vegetation index to investigate variability in island surface water area, an important link between climate variability and groundwater storage. Kiritimati surface water area varies seasonally, following wet and dry seasons, and interannually, due to hydroclimate variability associated with the El Niño/Southern Oscillation. The NIÑO3.4 sea surface temperature index, satellite-derived precipitation, precipitation minus evaporation, and local sea level all had significant positive correlations with surface water area. Lagged correlations show sea level changes and precipitation influence surface water area up to 6 months later. Differences in the timing of surface water area changes and variable climate-surface water area correlations in island subregions indicate that surface hydrology on Kiritimati is not uniform in response to climate variations. Rather, the magnitude of the ocean–atmosphere anomalies and island–ocean connectivity determine the extent to which sea level and precipitation control surface water area. The very strong 2015–2016 El Niño event led to the largest surface water area measured in the 18-year data set. Surface water area decreased to pre-event values in a similarly rapid manner (<6 months) after both the very strong 2015–2016 event and the 2009–2010 moderate El Niño event. Future changes in the frequency and amplitude of interannual hydroclimate variability as well as seasonal duration will thus alter surface water coverage on Kiritimati, with implications for freshwater resources, flooding, and drought.
15 Chapungu, L.; Nhamo, Luxon; Gatti, R. C. 2020. Estimating biomass of savanna grasslands as a proxy of carbon stock using multispectral remote sensing. Remote Sensing Applications: Society and Environment, 17:100275. [doi: https://doi.org/10.1016/j.rsase.2019.100275]
Carbon stock assessments ; Savannas ; Grasslands ; Biomass ; Estimation ; Remote sensing ; Climate change ; Greenhouse gas emissions ; Ecosystems ; Satellite imagery ; Landsat ; Models / Zimbabwe / Mashonaland / Shamva / Bindura
(Location: IWMI HQ Call no: e-copy only Record No: H049412)
(1.70 MB)
Limited research has been done to estimate the root biomass (belowground biomass) of savanna grasslands. The advent of remote sensing and related products have facilitated the estimation of biomass in terrestrial ecosystems, providing a synoptic overview on ecosystems biomass. Multispectral remote sensing was used in this study to estimate total biomass (belowground and aboveground) of selected tropical savanna grassland species. Total biomass was estimated by assessing the relationship between aboveground and belowground biomass, the Normalised Difference Vegetation Index (NDVI) and belowground biomass, and NDVI and total biomass. Results showed a positive significant relationship (p ¼ 0.005) between belowground and aboveground biomass. NDVI was significantly correlated (p ¼ 0.0386) to aboveground biomass and the Root Mean Square Error (RMSE) was 18.97 whilst the model BIAS was 0.019, values within acceptable ranges. A significant relationship (p ¼ 0) was found between belowground biomass and NDVI and the RMSE was 5.53 and the model BIAS was 0.0041. More so, a significant relationship (p ¼ 0.054) was observed between NDVI and total biomass. The positive relationships between NDVI and total grass biomass and the lack of bias in the model provides an opportunity to routinely monitor carbon stock and assess seasonal carbon storage fluctuations in grasslands. There is great potential in the ability of remote sensing to become an indispensable tool for assessing, monitoring and inventorying carbon stocks in grassland ecosystems under tropical savanna conditions.
16 Sawadogo, A.; Tim, H.; Gundogdu, K. S.; Demir, A. O.; Unlu, M.; Zwart, S. J. 2020. Comparative analysis of the pysebal model and lysimeter for estimating actual evapotranspiration of soybean crop in Adana, Turkey. International Journal of Engineering and Geosciences, 5(2):060-065. (Online first). [doi: https://doi.org/10.26833/ijeg.573503]
Evapotranspiration ; Crops ; Soybeans ; Irrigation water ; Satellite imagery ; Landsat ; Remote sensing ; Models ; Lysimeters / Turkey / Adana
(Location: IWMI HQ Call no: e-copy only Record No: H049544)
(0.98 MB) (0.98 MB)
Accurate estimation of evapotranspiration (ET) is an important factor in water management, especially in irrigated agriculture. Accurate irrigation scheduling requires accurate estimation of ET. The objective of this study was to estimate the actual evapotranspiration (ET a ) by the pySEBAL model and to compare it with the actual evapotranspiration measured by the lysimeter method of soybean crop in Adana, Turkey. Five Landsat 5 Thematic Mapper (TM) images and weather data were used for this study to estimate actual evapotranspiration by the pySEBAL model . The results showed a good relationship between ET a estimated by the pySEBAL model and ET a measured by the lysimeter method , with an R 2 of 0.73, an RMSE of 0.51 mm.day -1 , an MBE of 0.04 mm.day -1 and a Willmott's index of agreement ( d ) of 0.90. Based on this study, there is a good relationship between the actual evapotranspiration estimated by the pySEBAL model and the actual evapotranspiration measured by the lysimeter method. Consequently, ET a of soybean crop can be estimated with high accuracy by the pySEBAL model in Adana, Turkey.
17 Olivera-Guerra, L.; Merlin, O.; Er-Raki, S. 2020. Irrigation retrieval from Landsat optical/thermal data integrated into a crop water balance model: a case study over winter wheat fields in a semi-arid region. Remote Sensing of Environment, 239:111627. [doi: https://doi.org/10.1016/j.rse.2019.111627]
Water balance ; Models ; Satellite observation ; Landsat ; Irrigated sites ; Crops ; Wheat ; Soil water content ; Evapotranspiration ; Monitoring ; Drought stress ; Remote sensing ; Semiarid zones ; Case studies / Morocco
(Location: IWMI HQ Call no: e-copy only Record No: H049618)
(4.42 MB)
Monitoring irrigation is essential for an efficient management of water resources in arid and semi-arid regions. We propose to estimate the timing and the amount of irrigation throughout the agricultural season using optical and thermal Landsat-7/8 data. The approach is implemented in four steps: i) partitioning the Landsat land surface temperature (LST) to derive the crop water stress coefficient (Ks), ii) estimating the daily root zone soil moisture (RZSM) from the integration of Landsat-derived Ks into a crop water balance model, iii) retrieving irrigation at the Landsat pixel scale and iv) aggregating pixel-scale irrigation estimates at the crop field scale. The new irrigation retrieval method is tested over three agricultural areas during four seasons and is evaluated over five winter wheat fields under different irrigation techniques (drip, flood and no-irrigation). The model is very accurate for the seasonal accumulated amounts (R ~ 0.95 and RMSE ~ 44 mm). However, lower agreements with observed irrigations are obtained at the daily scale. To assess the performance of the irrigation retrieval method over a range of time periods, the daily predicted and observed irrigations are cumulated from 1 to 90 days. Generally, acceptable errors (R = 0.52 and RMSE = 27 mm) are obtained for irrigations cumulated over 15 days and the performance gradually improves by increasing the accumulation period, depicting a strong link to the frequency of Landsat overpasses (16 days or 8 days by combining Landsat-7 and -8). Despite the uncertainties in retrieved irrigations at daily to weekly scales, the daily RZSM and evapotranspiration simulated from the retrieved daily irrigations are estimated accurately and are very close to those estimated from actual irrigations. This research demonstrates the utility of high spatial resolution optical and thermal data for estimating irrigation and consequently for better closing the water budget over agricultural areas. We also show that significant improvements can be expected at daily to weekly time scales by reducing the revisit time of high-spatial resolution thermal data, as included in the TRISHNA future mission requirements.
18 Velpuri, Naga Manohar; Senay, G. B.; Schauer, M.; Garcia, C. A.; Singh, R. K.; Friedrichs, M.; Kagone, S.; Haynes, J.; Conlon, T. 2020. Evaluation of hydrologic impact of an irrigation curtailment program using Landsat satellite data. Hydrological Processes, 34(8):1697-1713. [doi: https://doi.org/10.1002/hyp.13708]
Irrigation water ; Water conservation ; Hydrological factors ; Evapotranspiration ; Landsat ; Satellite imagery ; Agriculture ; Water use ; Water availability ; Crops ; Precipitation ; Irrigated sites ; Lakes ; River basins ; Energy balance ; Models / USA / Oregon / Upper Klamath Lake Basin / Wood River / Sprague River / Williamson River
(Location: IWMI HQ Call no: e-copy only Record No: H049626)
https://onlinelibrary.wiley.com/doi/epdf/10.1002/hyp.13708
https://vlibrary.iwmi.org/pdf/H049626.pdf
https://vlibrary.iwmi.org/pdf/H049626.pdf
(7.52 MB) (7.52 MB)
Upper Klamath Lake (UKL) is the source of the Klamath River that flows through southern Oregon and northern California. The UKL Basin provides water for 81,000+ ha (200,000+ acres) of irrigation on the U.S. Bureau of Reclamation Klamath Project located downstream of the UKL Basin. Irrigated agriculture also occurs along the tributaries to UKL. During 2013–2016, water rights calls resulted in various levels of curtailment of irrigation diversions from the tributaries to UKL. However, information on the extent of curtailment, how much irrigation water was saved, and its impact on the UKL is unknown. In this study, we combined Landsat-based actual evapotranspiration (ETa) data obtained from the Operational Simplified Surface Energy Balance model with gridded precipitation and U.S. Geological Survey station discharge data to evaluate the hydrologic impact of the curtailment program. Analysis was performed for 2004, 2006, 2008–2010 (base years), and 2013–2016 (target years) over irrigated areas above UKL. Our results indicate that the savings from the curtailment program over the June to September time period were highest during 2013 and declined in each of the following years. The total on-field water savings was approximately 60 hm3 in 2013 and 2014, 44 hm3 in 2015, and 32 hm3 in 2016 (1 hm3 = 10,000 m3 or 810.7 ac-ft). The instream water flow changes or extra water available were 92, 68, 45, and 26 hm3, respectively, for 2013, 2014, 2015, and 2016. Highest water savings came from pasture and wetlands. Alfalfa showed the most decline in water use among grain crops. The resulting extra water available from the curtailment contributed to a maximum of 19% of the lake inflows and 50% of the lake volume. The Landsat-based ETa and other remote sensing datasets used in this study can be used to monitor crop water use at the irrigation district scale and to quantify water savings as a result of land-water management changes.
19 Yan, L.; Roy, D. P. 2020. Spatially and temporally complete Landsat reflectance time series modelling: the fill-and-fit approach. Remote Sensing of Environment, 241:111718. [doi: https://doi.org/10.1016/j.rse.2020.111718]
Satellite observation ; Landsat ; Monitoring ; Forecasting ; Farmland ; Modelling ; Time series analysis ; Satellite imagery ; Reflectance ; Uncertainty / USA / North Dakota / Minnesota / Michigan / Kansas
(Location: IWMI HQ Call no: e-copy only Record No: H049637)
https://www.sciencedirect.com/science/article/pii/S0034425720300870/pdfft?md5=82625844975a1237b706f251b7f62c7d&pid=1-s2.0-S0034425720300870-main.pdf
https://vlibrary.iwmi.org/pdf/H049637.pdf
https://vlibrary.iwmi.org/pdf/H049637.pdf
(21.70 MB) (21.7 MB)
Statistical time series models are increasingly being used to fit medium resolution time series provided by satellite sensors, such as Landsat, for terrestrial monitoring. Cloud and shadows, combined with low satellite repeat cycles, reduce surface observation availability. In addition, only a single year of data can be used where there is high inter-annual variation, for example, over many croplands. These factors reduce the ability to fit time series models and reduce model fitting accuracy. In solution, we propose a novel fill-and-fit (FF) approach for application to medium resolution satellite time series. In the ‘fill’ step, gaps are filled using a recently published algorithm developed to fill large-area gaps in satellite time series using no other satellite data. In the ‘fit’ step, a linear harmonic model is fitted to the gap-filled time series. The FF approach, and the conventional harmonic model fitting without gap filling, termed the F approach, are demonstrated using seven months of Landsat-7 and -8 surface reflectance Analysis Ready Data (ARD) over agricultural regions in North Dakota, Minnesota, Michigan, and Kansas. Synthetic model-predicted reflectance for days through the growing season are examined, and assessed quantitatively by comparison with an independent Landsat surface reflectance data set. The six Landsat reflective band root-mean-square difference (RMSD) between the predicted and the independent reflectance, considering millions of pixel observations for each ARD tile, show that the FF approach is more accurate than the F approach. The mean FF RMSD values varied from 0.025 to 0.026 for the four tiles, whereas the mean F RMSD values varied from 0.026 to 0.047. These mean FF RMSD values are <0.03 which is comparable to the uncertainty specification for the Landsat 8 OLI TOA reflectance, but greater than the atmospheric correction uncertainty in any Landsat 8 OLI band. The greatest RMSD values were found over the Minnesota tile and occurred due to a long period of missing data early in the growing season, and the smallest RMSD values were found for the Kansas tile because of the high availability of clear surface observations. The F approach could not be applied where there were insufficient clear surface observations to fit the model, and where the model was applied, the fitting was often sensitive to issues including gaps in the Landsat time series and the presence of undetected cloud- and shadow-contaminated observations. The FF approach could be applied to every ARD tile pixel location and the predicted reflectance was spatially-coherent and natural looking. Examples are shown that illustrate the potential of using FF predicted synthetic reflectance time series for land surface monitoring.
20 Pocas, I.; Calera, A.; Campos, I.; Cunha, M. 2020. Remote sensing for estimating and mapping single and basal crop coefficientes: a review on spectral vegetation indices approaches. Agricultural Water Management, 233:106081. [doi: https://doi.org/10.1016/j.agwat.2020.106081]
Remote sensing ; Crops ; Water requirements ; Evapotranspiration ; Vegetation index ; Irrigation management ; Soil water balance ; Soil moisture ; Earth observation satellites ; Landsat ; Geographical information systems ; Monitoring ; Water stress ; Mapping ; Models
(Location: IWMI HQ Call no: e-copy only Record No: H049654)
(0.77 MB)
The advances achieved during the last 30 years demonstrate the aptitude of the remote sensing-based vegetation indices (VI) for the assessment of crop evapotranspiration (ETc) and irrigation requirements in a simple, robust and operative manner. The foundation of these methodologies is the well-established relationship between the VIs and the basal crop coefficient (Kcb), resulting from the ability of VIs to measure the radiation absorbed by the vegetation, as the main driver of the evapotranspiration process. In addition, VIs have been related with single crop coefficient (Kc), assuming constant rates of soil evaporation. The direct relationship between VIs and ET is conceptually incorrect due to the effect of the atmospheric demand on this relationship. The rising number of Earth Observation Satellites potentiates a data increase to feed the VI-based methodologies for estimating and mapping either the Kc or Kcb, with improved temporal coverage and spatial resolution. The development of operative platforms, including satellite constellations like Sentinels and drones, usable for the assessment of Kcb through VIs, opens new possibilities and challenges. This work analyzes some of the questions that remain inconclusive at scientific and operational level, including: (i) the diversity of the Kcb-VI relationships defined for different crops, (ii) the integration of Kcb-VI relationships in more complex models such as soil water balance, and (iii) the operational application of Kcb-VI relationships using virtual constellations of space and aerial platforms that allow combining data from two or more sensors.
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