Your search found 2 records
1 Imholt, C.; Soulsby, C.; Malcolm, I. A.; Hrachowitz, M.; Gibbins, C. N.; Langan, S.; Tetzlaff, D. 2011. Influence of scale on thermal characteristics in a large Montane River Basin. River Research and Applications, 17p. (Online first). [doi: https://doi.org/10.1002/rra.1608]
River basins ; Streams ; Temperature ; Regression analysis ; Models ; GIS ; Monitoring ; Catchment areas ; Riparian zones ; Vegetation / UK / Scotland / River Dee Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H044701)
(4.69 MB)
This study monitored stream temperatures over two hydrological years at various nested scales within the large, unregulated river Dee catchment (North East Scotland). These scales were (i) the whole catchment (11 sites along main stem Dee); (ii) the tributary (single sites in main tributaries); (iii) the Girnock (five sites in one subcatchment); and (iv) the reach (26 points across single reach). The aim was to characterize the thermal regime of all locations and compare the magnitude of variation between each scale. The controls on this variation were assessed via a multiple linear regression model using Geographic Information System-derived catchment data. Temperatures were collected at 15-min resolution and for further analysis and discussion combined to daily means. At the catchment and subcatchment scales, a west to east gradient in mean and minimum temperatures was observed, largely paralleling changes in altitude. Temperature differences between subcatchments were generally greater than between the sites along the main stem of the Dee. Differences between tributaries reflected differences in their morphology and land use. However, some tributaries had similar thermal regimes, despite different catchment and riparian characteristics. Subcatchment differences in thermal regimes of one of the tributaries corresponded to riparian vegetation reduced diurnal variability in sections dominated by broadleaf woodland. Compared with the larger scales, reach differences in thermal regime were small (e.g. mean temperatures of riffle, pool and margin habitats were within 0.3C). The most noticeable difference was in relation to the point samples within the backwater area, which has a more constant thermal regime, most probably reflecting its groundwater source. The regression analysis indicated that monthly mean temperatures can be predicted well using elevation and catchment area. Forest cover was a significant explanatory variable during the summer months. However, some of the empirical temperature data from the Dee indicate that similar thermal regimes can result from different physical controls and processes that have important implications for the extrapolation of such predictive models.
2 Hulsman, P.; Savenije, H. H. G.; Hrachowitz, M.. 2021. Satellite-based drought analysis in the Zambezi River Basin: was the 2019 drought the most extreme in several decades as locally perceived? Journal of Hydrology: Regional Studies, 34:100789. [doi: https://doi.org/10.1016/j.ejrh.2021.100789]
Drought ; River basins ; Reservoirs ; Water storage ; Water levels ; Precipitation ; Evaporation ; Rain ; Satellite observation ; Semiarid zones / Zambia / Zambezi River Basin / Kariba Dam
(Location: IWMI HQ Call no: e-copy only Record No: H050294)
https://www.sciencedirect.com/science/article/pii/S2214581821000185/pdfft?md5=b199f7eb1055b5e8e7be18d9d7f56f05&pid=1-s2.0-S2214581821000185-main.pdf
https://vlibrary.iwmi.org/pdf/H050294.pdf
https://vlibrary.iwmi.org/pdf/H050294.pdf
(5.53 MB) (5.53 MB)
Study region:
The study area is the river basin upstream of the Kariba dam located in the Zambezi River at the border of Zambia and Zimbabwe.
Study focus:
During the dry season of 2019 in Sub-Saharan Africa, extremely low water levels occurred in the Zambezi. According to news media, locals perceived this drought as the worst in several decades. We analyzed the 2019 drought in the Zambezi River Basin upstream of the Kariba dam to determine whether it indeed was the longest, most intense, and severe drought, in terms of precipitation, total water storage and reservoir water level observations over recent decades.
New hydrological insights for the region:
Data analysis indicates that the 2019 drought indeed had the lowest basin-averaged annual rainfall, most severe local rainfall deficit in the north of the basin, and lowest reservoir level since 1995. However, the rainfall deficit was more severe in 2002, both basin-wide and locally in the south of the basin. The total storage deficit was more severe in 2004, both basin-wide and locally in the central part of the basin. However, as the available storage data did not cover the entire deficit for 2019, its final duration and severity remain unknown. Therefore, it depends on the drought characteristic, hydrological variable, and location within the basin, whether the 2019 drought was indeed the most extreme over recent decades.
The study area is the river basin upstream of the Kariba dam located in the Zambezi River at the border of Zambia and Zimbabwe.
Study focus:
During the dry season of 2019 in Sub-Saharan Africa, extremely low water levels occurred in the Zambezi. According to news media, locals perceived this drought as the worst in several decades. We analyzed the 2019 drought in the Zambezi River Basin upstream of the Kariba dam to determine whether it indeed was the longest, most intense, and severe drought, in terms of precipitation, total water storage and reservoir water level observations over recent decades.
New hydrological insights for the region:
Data analysis indicates that the 2019 drought indeed had the lowest basin-averaged annual rainfall, most severe local rainfall deficit in the north of the basin, and lowest reservoir level since 1995. However, the rainfall deficit was more severe in 2002, both basin-wide and locally in the south of the basin. The total storage deficit was more severe in 2004, both basin-wide and locally in the central part of the basin. However, as the available storage data did not cover the entire deficit for 2019, its final duration and severity remain unknown. Therefore, it depends on the drought characteristic, hydrological variable, and location within the basin, whether the 2019 drought was indeed the most extreme over recent decades.
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