| China belongs to continental monsoon climate zone and has three steps of topography. In this context, the drought occurs frequently and effects widely. Due to the climate change and human activity, the drought has become more serious. On the one hand, global warming has produced an increase of intensity and frequency. On the other hand, the exposure and vulnerability of drought disaster has increase sharply because of social and economic development. The social and economic development and ecological civilization construction are hindered by drought disaster. Drought disaster is the key issue in coping climate change and natural hazard. The disaster-causing factors, object of hazard effect and disaster-forming environment are dynamic. There are multiple temporal and spatial scale and random. The trends in history and future are different, so we cannot use the history law to guide the risk-management in the future entirely. In order to meet the need of social and economic development and water environment security in the future, it is important to answer four questions in term of risk. How to estimate drought and its risk? How have they changed in past? How will they change in the future? How can we cope with the drought risk?The study took Luanhe River Basin as the study area. With the simulation results of hydrological model as well as water supply and demand, the drought magnitude was evaluated in term of water resources system. The spatiotemporal variation characteristics of drought severity, areal extent and frequency were also analyzed. Based on four-factor theory of disaster risk-forming and fitting method of hazard loss, the study put forward the method of drought risk evaluation and applied in study area to identify the spatiotemporal variation characteristics of drought risk. The study also project drought risk in the future with the relative optimum outputs of Global Climate Models (GCMs). Previously, the selection method of GCMs based on the statistical distribution characteristics was built. Occurring to the drought risk in the future and three layers of risk assessment method, the corresponding strategies to drought risk in Luanhe River Basin were discussed. The main conclusions in this paper are as follows:(1) During 1973-2012, the area of mild drought and moderate drought had an obvious increasing trend, while the area of severe drought and extreme drought had a decreased trend, but the trend was not significant. From an overall perspective, the general trend of drought area was decreasing-increasing-decreasing. The drought problem was serious in 1980s and 2000s. The drought area were 1.3-1.4 times than other decades. The drought mainly appeared in hilly and mountainous area of middle reaches, such as Longhua, Luanping, Chengde and Kuangcheng. In the study area, the drought magnitudes were mainly mild and moderate. The areas of cultivated land which the mild and moderate frequent were more than 20% were 6305km2 and 3937 km2, accounting for 61.5% and 38.4% of the whole cultivated land.(2) The higher drought risk areas were located in Guyuan, Fengning, Duolun, Weichang, Longhua, Chengde, Pingquan. While drought risk in the right area of middle reaches and plain of lower reaches was lower. The overall situation of drought risk in Luanhe River Basin remained serious. Sixty-five percent of the cultivated land was in the moderate and above drought risk area. Over the last 20 years, the magnitude of higher risk area was decreased while the magnitude of lower drought risk area was increased. Due to Land Use/Cover Change, the risk magnitude in 30% cultivated land increase by 1 level. The area of moderate-high risk and above was increased by 14.2%.(3) Under the influence of climate change, the areas of moderate risk and high risk will expand, especially in left area of middle reaches, such as the north of Chengde. More specifically, during 2020-2050, the area of cultivated land in moderate risk will be 1996-3203 km2, accounting for 18.2-29.2% of whole cultivated land. It is 1.4-2.1 times than baseline period (1961-1990). The area of cultivated land in high risk will be 3576-3711 km2, accounting for 29.8-33.8% of whole cultivated land. It is 1.9-2.2 times than baseline period. The overall situation of drought risk will be more serious as the area of moderate-high risk and above will increased by 19.1-29.8%. The risk magnitude increase by 1 level in 27.1-44.5% cultivated land. It increase by 2-3 level in 7.5-11.8% cultivated land. The increased risk areas are mainly in Chengde, Longhua, Luanping and Zunhua. The risk magnitude will remain unchanged in the half of cultivated land. These areas are mainly in the upper reaches and left area of lower reaches.(4) The key areas of risk treatment are in the upper reaches and left area of middle reaches. If the green for grain project is implemented in the region which is not suitable for farm and the area of cultivation is decreased, the area of cultivated land in moderate risk and above could decreased by 39.5% and the value of crop in the context of drought could increase by 3.1% in control region. After this, if the farmland to ensure stable yields in drought and waterlogging increased by 9.1% in control region benefited from water project, such as Longhua, east of Chengde and Kuancheng, the area of cultivated land in moderate risk and above could decreased by 21.6% and the value of crop in the context of drought could increase by 3.0% any further.The innovations of this paper are reflected in three aspects:(1) In the assessment of drought disaster risk, the drought assessment model was built by simulain results from hydrologic model and water demand.It can comprehensively reflect the effect of water deficit and duration on drought magnitude. Besides, the drought disaster risk assessment model was built based on four-factor theory of disaster risk-forming and fitting method of hazard loss, which took the crop loss into consideration.The model can describe the drought disaster risk objectively.(2) In the prediction of drought disaster risk, the performance of GCMs was assessed according to the probability distribution characteristic of outputs. And the future prediction results were ensambled by relative optimal model. The new dataset was used to predict the drought disaster risk in the future. The method is more suitable for extreme events prediction than muti-average method.(3) In the treatment of drought disaster risk, this study used the layer-by-layer mode.The socio-economic systems adaptive performance and engineering system were combined according to regulatory characteristics of risk factors.With this method, the key regions and links of risk coping as well as region to withstand the risk can be identified. |
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