Evaluation Of Eco-hydrological Effect Of Compound Erosion Of Pisha Estimation Models In Pisha Sandstone Region

Pisha sandstone is distributed in the border areas of the three provinces called Inner Mongolia,Shanxi and Shaanxi.And the Pisha Sandstone region has extremely serious soil and water loss,which is the main source of coarse sediment in the middle reaches of the Yellow River and is called as "Cancer of the global ecology" by relevant scholars.As a result,the region needs to be treated urgently.Evapotranspiration is an important part of the eco-hydrological cycle process and an important expense of water balance.However,there are few reports about researches of evapotranspiration in Pisha sandstone region currently.In this paper,different types of Pisha sandstone region which is represented by Erlaohu-gully small watershed,Tela-gully small watershed and Shawurtai-gully small watershed were studied.And five models which contain Blaney-Criddle(BC),Hargreaves(HG),Remanenko(RN),Makkink(MK),and World Meteorological Organization(WMO)were selected to evaluate the applicability.Coefficients of the models were modified based on the measured data and the results of the FAO Penman-Monteith(FAO P-M)model as well.The main conclusions are:1)The actual evapotranspiration and potential evapotranspiration of the three types of Pisha sandstone region are all reach the maximum value in late May or early June in the whole year and December on the contrary,and evapotranspiration of Erlaohu-gully(the soil covered type)is higher than that in Shawurtai-gully(the bare land type),and the diference from the potential evapotranspiration of the same watershed is less,which indicates that the ability of evapotranspiration in soil covered type is stronger than that of bare land type;2)Evapotranspiration per unit area of grassland and bare land is much higher than that of forest;3)The applicability of unmodified models in Pisha sandstone region is:MK>WMO on the daily scale;MK>BC>HG>WMO on the ten-day scale;MK>BC>HG>WMO>RN on the monthly scale,while that of modified models is:MK>WMO on the daily scale;MK>HG>BC>WMO on the ten-day scale;MK>HG>BC>WMO>RN on the monthly scale,but RN is better than BC and WMO without considering absolute deviation;4)It is recommended to use the modified MK model as a simplified model for FAO P-M,but the modified WMO model shouldn't be used for the estimation of actual evapotranspiration,however,it is recommended to use potential evapotranspiration to approximately replace the actual evapotranspiration instead while modified 10-day and monthly scale models could be used to calculate the actual evapotranspiration estimation in Pisha sandstone region.