Study On Drought Monitoring Technology Of BEPS Model Based On The Simulation Of Land Surface Evapotranspiration

In recent years, in the background of climate change characterized by global warming, extreme weather events have increased and enhanced.Drought is one of the main meteorological disasters, it has caused a great threat to grain production in the world. Various countries have carried out relevant research on drought monitoring from hydrological, meteorological and agricultural perspective,and proposed various drought monitoring index and method. Compared with the traditional method of drought monitoring, remote sensing drought monitoring based on soil moisture and closely related with characteristics physical inversion, which can be described temporal and spatial variationon the surface water status. And at the same time, to achieve the purpose of drought monitoring with the appropriate indicators. Land surface evapotranspiration (ET) as an important part of water and energy balance of the surface, has important contact with soil moisture. BEPS (Boreal Ecosystem Productivity Simulator) model is a process of considering carbon and water cycles in ecological system.And it’s a process model that combine remote sensing technology and mechanism of ecological model. This study localizates and validates the BEPS model, and then simulates and quantitative analyzes the temporal and spatial variation characteristics of terrestrial ecosystems evapotranspiration in the United States of America in2007-2009. On this basis, to build BMI index module, which is applied to the regional drought monitoring business..The study also analyzes and discusses the feasibility of the model in regional drought monitoring application, tries to establish a system of drought monitoring technology based on the model.The study can be provided the technical reference for the future use of the technology development of Chinese regional drought monitoring. The main conclusions are as follows:(1) First both of the AmeriFlux data and land surface flux simulation results from Atmosphere Land Exchange Inverse model (ALEXI)are used to find the evapotranspiration simulation reliability and adaptability in the United States. The result shows that BEPS model has a good simulation of regional surface ET research, which provides an effective and reliable method for the simulation of the United States forest ecosystem ET research.(2)According to the localization of BEPS model, we analyzed the temporal and spatial distribution characteristics of evapotranspiration simulation in2007-2009. The results showed that, evapotranspiration, precipitation, and LAI have obvious seasonal variation characteristics. From the time period, precipitation, LAI and evapotranspiration reached the highest value in the growing season of vegetation, but the lowest in the non-growing season. The overall shows a single peak trend. The value of ET reaches an average of505mm·a-1in2007-2009, and the highest value of1667mm·a-1. According to the spatial scale, evapotranspiration decreased gradually with the increasing of latitude,.while evapotranspiration varies from high to low with the increased longitude, which has inseparable reasons with these factors such as precipitation, vegetation cover and temperature etc.(3)According to the different influences of different impact factors on evapotranspiration, we quantitatively analyze the influence of several factors, including leaf area index(LAI), precipitation and temperature. The result shows that, the influence of LAI on ET in the eastern is larger than the one in the west, the impact of precipitation on ET is biggest in the central, and then the east, the smallest one is in the west, and the biggest value of influence of temperature on evapotranspiration is mainly distributed in the east, while the minimum value is mainly in the west.Through the sensitivity analysis of the influence of different impact factors on evapotranspiration in the same area,we find that LAI has the strongest sensitivity on evapotranspiration on the whole.(4) According to the simulation results of evapotranspiration based on the BEPS model, we constructe the BMI index and then analyze the time and spatial and temporal distribution characteristics of dry and wet conditions in the United States. The result shows that, spatial and temporal distribution characteristics of regional evapotranspiration, precipitation and BMI value have obvious seasonal variation, and during the year, the trends of precipitation and evapotranspiration are relatively consistent, while precipitation is negatively correlated with BMI, especially the changes in the growing season. Compared with dry index, the dry and wet conditions are the same instructions. From the drought effect indicates at different time scales, the month time and the seasonal time scalcale is the best, the week scale is the last.Analysis of the correlation with USDM, BMI index has advantages over the Palmer Z index and SPI index in a short period of time, and its calculation process is relatively simple, and suitable for drought monitoring in a wide range of areas. Fully shows that, the index constructed on the simulate evapotranspiration of BEPS model is feasible in drought monitoring.