Analysis Of The Spatio-Temporal Variability Of Water And Energy In The Agricultural-Pastoral Ecotone Of Northwest China

In recent years,the agricultural-pastoral ecotone in Northwest China has experienced a significant warming trend.The intensity of human activities has increased significantly.Frequent extreme temperatures and precipitation events have caused the temporal and spatial distribution of moisture and heat in the ecologically fragile northwest agricultural-pastoral zone.A series of corresponding changes had a very serious impact on the balance of the ecosystem in the study area,the regional hydrological cycle,human production and livelihood,and the production and development of agriculture and animal.It is vital to understand the climatic variability and the persistence of the region to prepare for and mitigate future disastrous events.The study selects the junctions of Shaanxi,Ningxia and Inner Mongolia as the research area.The area is a microcosm of the eco-environmentally fragile agro-pastoral ecotone in Northwest China.This study used the datasets of precipitation,air temperature,sunshine hours,average relative humidity,vapor pressure,and wind speed from the 10 meteorological stations in and around the study area from 1960 to 2016 to calculate reference crop evapotranspiration based on the modified Penman-Monteith formula?ET₀?and surface moisture index?W?,combining with precipitation and air temperature,to study the spatial and temporal distribution features of climate,heat and water in the region.The main findings are as follows:?1?During the period from 1960 to 2016,the increase of temperature in the study area was very significant.The precipitation and surface moisture index showed a weak downward trend overall,and ET₀ showed a slight upward trend.The hydrothermal pattern of the entire study area had changed from 1990 to 2000:Temperatures had undergone significant upward in the 1990s,and the warming trend became more pronounced;the precipitation and moisture indices showed evident changing pattern around the year 2000.The change had changed from the original declining trend to the increasing trend;after the ET₀ dropped around 2000,it changed from the originally fluctuating upward trend to the downward trend.The primary cycle of precipitation,temperature and ET₀ are 3,8 and 27 years?2?At the seasonal scale,the most significant change in hydrothermal pattern is in winter:the temperature had increases 0.54?every 10 years in winter.This trend has been exacerbating;while the precipitation has decreased in the other three seasons,Precipitation in winter showed a rising trend;in winter,ET₀ showed a significant upward trend,was significant at?=0.10.The second obvious change is summer:the decreasing trend of precipitation in summer is the most obvious,was significant at?=0.10.The rising trend of temperature is the smallest in the four seasons,but ET₀shows a decreasing trend.The hydrothermal changes in the spring and autumn are generally flat.?3?The distribution of the east-west water and heat distribution in the study area is relatively obvious.The eastern region as a whole is characterized by high temperatures,heavy precipitation,less evapotranspiration,and humid conditions,and the climate is warmer and wetter than the west.The spatial pattern of hydrothermal changes shows that the temperature,ET₀,and surface moisture index tend to be uniform.areas with lower temperatures shows an increasing pattern while areas with higher temperatures shows a decreasing pattern;however,the precipitation shows a trend of polarization,areas with higher precipitation shows an increasing pattern while areas with lower precipitation shows a decreasing pattern.?4?In the study area,there is a phenomenon of evaporation paradox in the summer and in western regions.Agricultural development is mainly distributed in southeast areas with higher average temperature,higher precipitation,lower reference crop evapotranspiration,and higher moisture index.In the future,the temperature,precipitation,and ET₀ of the study area show increasing persistence,indicating the climate in the future of the study area will become warmer and wetter in the short term.