Study On Driving Mechanism And Assessment Methods Of Drought

Drought, as a natural phenomenon which has been disturbing us for a long time, has attracted wide attention in the field of weather, hydrology, agriculture and ecological environment. The driving mechanism and influence of climate change and human activities on drought has become the hotspot in scientific research as well as the great challenge to the sustainable development of our economy and society. The research on driving mechanism and the assessment method is of great demand in coping with drought, guaranteeing the national water resource security and supporting sustainable development to our economy and society.Drought can be divided into meteorological drought, hydrological drought and agricultural drought from different perspectives, which can be considered as the reflection of natural-artificial dualistic characteristics of hydrological cycle anomaly. Based on the theory of natural-artificial dualistic characteristics of hydrological cycle, climatic system and physiological ecology of crop, the drought driving factors of meteorological drought, hydrological drought and agricultural drought were identified and the driving mechanism were investigated in this study. The quantitative analysis of drought driving was conducted through building drought evaluation index and improving assessment method of drought. It is verified in typical watershed using the simulation platform designed. The main contents of this thesis can be concluded as follows:1) The research progress of the driving mechanism of drought and assessment method at home and abroad is summarized.The research progress of drought driving mechanism, assessment method and the analysis of driving mechanism are summarized and the issue in urgent need to be addressed is proposed. Then, the main research contents and technical route are outlined.2) The driving mechanism of meteorological drought, hydrological drought and agricultural drought is discussed.Based on the understanding of the definition of drought, the concepts of the three kinds of drought are defined and the process of evolution, buffering, beginning, developing and relieving of drought is analyzed. The driving mechanism and factors of meteorological drought, hydrological drought and agricultural drought are discussed. The changes of atmospheric circulation anomaly and underlying surface are the main driving factors of meteorological drought. The climatic variation, land use change and water resources development are the principal factors of hydrological drought and agricultural drought.3) The evaluation indexes of hydrological drought based on full-aperture water resource were proposed, the indexes of meteorological drought and agricultural drought were optimized and the assessment method of drought was improved.The theoretical framework of drought is put forward according to data preparation, index calculation of drought and statistic analysis. The evaluation indexes of hydrological drought based on full-aperture water resource were proposed, the indexes of meteorological drought and agricultural drought were optimized and the calculation methods of drought duration, area, intensity, frequency and other characteristic indexes. Then, the characteristic analysis of drought was systematically summarized from the aspects of single variable, bivariate and multivariable. Finally, the assessment method of drought can be achieved programmatically.4) The drought driving analysis framework based on driving force-pressure-status-response model was established and the method of quantitative drought driving analysis was put forward.A drought driving analysis framework based on driving force-pressure-status-response model was established from the perspective of systematic idea. The principal driving factors were quantified through combining the result of drought driving mechanism. What’s more, the analysis methods of drought driving factors variation were summarized. The drying force and pressure of drought formation and evolution system were determined. Subsequently, the drought driving scheme was established. The drought evaluation indexes of comprehensive response were established through the combination of drought characteristic indexes and related relationships. The analysis method of climatic drought driving was proposed based on statistics. The simulation platform was established based on the water cycle model WACM and assessment methods of drought. The quantitative analysis method considering the influence of change of climate, land use and the exploitation and utilization of water resources on hydrological drought and agricultural drought was put forward.5) The temporal-spatial distribution discipline of the northern Haihe River basin is assessed.The northern Haihe River was divided into4619hydrological response unit for water cycle simulating. WACM model is calibrated and verified based on the observed data from1951to2009, and the water cycle process from1956to2009was simulated. The meteorological drought, hydrological drought and agricultural drought were evaluated by drought evaluation methods using the measured weather data and simulated data. The temporal-spatial distribution discipline and the relationship among three kinds of drought in the northern Haihe River basin is assessed.(1) There were159meteorological drought events from1951to2009, with average drought duration of2.5months, average drought area of54%and average drought intensity of0.85. The meteorological drought events focused on the area of drought duration from1to3months, drought area from30%to70%and drought intensity from0to1.(2) There were34hydrological drought events from1951to2009, with average drought duration of16months, average drought area of24%and average drought intensity of3.25. The hydrological drought events focused on the area of drought duration from1to20months, drought area from5%to25%and drought intensity from0to6.(3) There were102agricultural drought events from1951to2009, with average drought duration of4.8months, average drought area of40%and average drought intensity of1.13. The agricultural drought events focused on the area of drought duration from1to8months, drought area from30%to50%and drought intensity from0to3.(4) The marginal probability distribution of drought duration, area and intensity was fitting by exponential distribution, normal distribution and Γ distribution. Copula formula which was optimized by SED is used to analysis the simultaneous distribution of drought duration-area, drought duration-intensity. The probability distribution is obtained and the contingent probability and recurrence interval are calculated.(5) The drought duration among meteorological, hydrological and agricultural drought presented obvious linear correlation relationship. The intensity of meteorological drought and hydrological drought shows significant correlation, but the intensity of meteorological and agricultural drought had no significant correlation, because irrigation weakens the correlation between meteorological and agricultural drought intensity. The drought area of meteorological, hydrological and agricultural drought had no significant correlation. The agricultural drought is more serious in non-irrigated area than that in irrigated area.6) The drought driving results and the coping strategies of the northern Haihe River basin are studied.Based on the data from1951to2009and the change rule of drought driving factors, the reference period and influence period are defined and the driving effect of meteorological drought, and agricultural drought, hydrological drought are analyzed. And some coping strategies are proposed to deal with the drought.(1) The results of climate factor variation analysis show that the precipitation, sunshine time, wind speed, relative humidity has a decrease tendency but temperature has an increase tendency, and the abrupt change points of all factors concentrated in the1980s. The human activities interference increases quickly after1970. Considering the comprehensive role of climate change and human activities, the reference period was from1951to1970, the transitional period was from1971to1989and the influence period was from1990to2009.(2)Precipitation was the most sensitive factor for meteorological drought, and then followed by sunshine duration, relative humidity, atmospheric temperature and wind speed. Drought can be more serious with the decreasing of precipitation, sunshine duration, relative humidity, and wind speed and the increasing atmospheric temperature. The aggregative indicator of drought duration, area and intensity increased10%,7%,21%and18%with the decreasing10percent of precipitation.(3)The influence of climatic variation, land use change and water resources development and utilization to meteorological drought are57%,33%and10%respectively.(4)The influence of climatic variation, land use change and water resources development and utilization to agricultural drought are40%,4%and-56%respectively. The results show that water resources development and utilization can lessen the effects of drought.(5)Some coping strategies are proposed to abate the drought, such as building the monitor system scientifically, reinforcing the construction of water infrastructure and strengthening ecological environmental protection, and so on.