No abstract

Accurate estimation of evapotranspiration (ET) is essential in water resources management and hydrological practices. Estimation of ET in areas, where adequate meteorological data are not available, is one of the challenges faced by water resource managers. Hence, a simplified approach, which is less data intensive, is crucial. The FAO‐56 Penman–Monteith (FAO‐56 PM) is a sole global standard method, but it requires numerous weather data for the estimation of reference ET. A new simple temperature method is developed, which uses only maximum temperature data to estimate ET. Ten class I weather stations data were collected from the National Meteorological Agency of Ethiopia. This method was compared with the global standard PM method, the observed Piche evaporimeter data, and the well‐known Hargreaves (HAR) temperature method. The coefficient of determination (R2) of the new method was as high as 0.74, 0.75, and 0.91, when compared with that of PM reference evapotranspiration (ETo), Piche evaporimeter data, and HAR methods, respectively. The annual average R2 over the ten stations when compared with PM, Piche, and HAR methods were 0.65, 0.67, and 0.84, respectively. The Nash–Sutcliff efficiency of the new method compared with that of PM was as high as 0.67. The method was able to estimate daily ET with an average root mean square error and an average absolute mean error of 0.59 and 0.47 mm, respectively, from the PM ETo method. The method was also tested in dry and wet seasons and found to perform well in both seasons. The average R2 of the new method with the HAR method was 0.82 and 0.84 in dry and wet seasons, respectively. During validation, the average R2 and Nash–Sutcliff values when compared with Piche evaporation were 0.67 and 0.51, respectively. The method could be used for the estimation of daily ETo where there are insufficient data. Copyright © 2013 John Wiley & Sons, Ltd.

Landscape response to drivers of change is more visible and noticeable in deltas and floodplains than in upstream. Here, we address the changes of Lake Tana basin by investigating the delta development of Gumara River and sediment deposition in the Fogera floodplain over a 58‐year period when agricultural land expanded, agriculture intensified, and flooding of the alluvial plain became more frequent. Old maps show that delta formation before the 1950s was minimal, indicating that the sediment contributed by the rivers to the lake was small. However, during the last 58 years, the delta has expanded continuously. When considering the same lake level (2·68 m) from 1984 to 2014, the delta has expanded an average of 5 ha annually, and by considering different lake levels and corresponding delta areas, the delta increased in height an average of 3 cm annually. While the growth of the delta was approximately linear, the sediment concentration in the river doubled in the last 30 years, indicating more efficient sediment trapping in the floodplain as a result of higher lake levels, rising river beds, and farmers intervening with the course of the river near the shore. Unless effective river restoration and catchment‐based treatment measures are put in place, the capacity of the rivers will further reduce and aggravate the flooding of the floodplain, causing more sediment deposition in the river channel and on the floodplain. Copyright © 2016 John Wiley & Sons, Ltd.