Drought is recognized as a natural hazard and environmental disaster and it has caused extensive impact during recent decades over the worldwide [1
], such as the North America [3
], Europe [5
], Australia [7
], Africa [8
], and the Asia [10
]. Drought is usually caused by the scarcity of precipitation, coupled with water evaporation, and water consumption expenditure. Drought affects both surface and underground water resources and can lead to reduced water supply, water storage of water conservancy projects, social and economic water use, and ecological environment water use [13
]. The lack of water will lead to the destruction of crop water balance and the reduction of crop yield or poor harvest [14
], resulting in food problems and even starvation. Drought can also affect ecosystems stability [15
] and even kill animals due to a lack of adequate drinking water during severe drought seasons. In recent years, especially in the face of increasing population, agricultural expansion, and industrial and economic development, other aspects of water demand continue to increase, drought will have an important impact on all these aspects [9
]. Therefore, drought needs to arouse extensive attention by the human society.
Climate change is a universal consensus of the global scientific community and the public. Recent and potential future increases in global temperature are likely to be associated with the hydrologic cycle, which brings the changes to precipitation and thus increases extreme events such as droughts [16
]. Many studies have shown that the drought situation may be changed and even more severe in the face of global and regional climate change throughout different global or regional climate models, emission scenarios, time periods, and drought indicators. Dai [17
] has found that the global aridity has increased substantially since the 1970s and the climate models project increased aridity in the 21st century over most of Africa, southern Europe, the Middle East, most of the American continent, Australia, and Southeast Asia. Liu et al. [18
] revealed that there would be an increasing drought risk if the global warming continues to rise at a high level. Ahmadalipour et al. [9
] took an ensemble of 10 regional climate models and a multi-scalar drought index to quantify drought hazard and found that drought risk in Africa is expected to increase in future with varied rates for different models and scenarios. Meanwhile, different regions and basins will inevitably show different characteristics of drought under the influence of climate change because of the differences in geographical location and economic development scale. Calanca [19
] revealed that in the future the Alpine region would suffer an increasing drought frequency and a higher drought severity under the climate scenario of a SRES A2 emission pathway. Leng et al. [20
] indicated that droughts would become more severe, prolonged, and frequent for 2020–2049 relative to 1971–2000 in vast areas of China. Meanwhile, even in the same region, drought characteristics would be different for choosing the different global or regional climate models and emission scenarios [21
] or selecting the different drought indicators [22
]. Therefore, it is necessary to continue carrying out in-depth and systematic drought research to different regions or basins in order to lay a foundation for the local scientific disaster prevention and mitigation responses and measures.
China is a frequently drought-affected country in East Asia since the precipitation and temperature changes significantly from one region to another region [20
]. Huai River Basin (HRB) is a typical large basin in eastern China and it situated in the middle of the North-South climatic transition zone, which is also one of the most important bases for agriculture production in China. Because of its special geographical location and climatic type, drought and flood have changed dramatically and occurred frequently, which have an important impact on the ecological systems, regional food production security, economy, and the society. In recent decades, with the background of global climate change, the hydrothermal conditions in the HRB have also changed. Some studies reveal that a future increase in evapotranspiration would happen and affect the current humid region south of the HRB retreating southward and changing to a sub-humid region [24
]. Yang et al. pointed out that the trend of flood and drought events in the HRB was positively related to climate warming with a higher coefficient of determination [25
]. Li et al. also found that drought is expected to rise in frequency, duration, severity, and intensity in the HRB from 2010 to 2099 [26
]. The previous studies have shown that the watershed water cycle would be altered under the climate change and then influence the drought conditions. However, it should note that climate change is uncertain. The differences in describing future hydrothermal conditions under different climate models will directly affect the future drought management. As an important food and industrial production area in China, it is necessary to consider the future drought development under different climate change patterns and emission scenarios in order to cope with potential disaster risks.
Climate models are important tools for studying climate change and its impacts on drought. Climate model has the remarkable ability of simulating the time evolution of average climate characteristics and climate variability. Up to now, there are many global climate models and regional climate models (RCMs) for studying climate change mechanism and exploring climate change factors. A series of GCMs can well simulate the average characteristics of large-scale grids, as well as the characteristics of near-surface temperature, high-level atmospheric field, and atmospheric circulation. The basic idea of RCMs is to nest the RCM into the GCM step by step. The GCM provides the initial field and lateral boundary conditions. The global circulation models (GCMs) of the Coupled Model Intercomparison Project phase 5 (CMIP5) climate models were designed to advance the knowledge of climate variability and climate change by the World Climate Research Programme’s (WCRP) Working Group on Coupled Modelling (WGCM) [27
]. It provided an important scientific basis for detecting the impact of human activities on historical climate change. CMIP5 have been improved in many aspects comparing with previous generations of CMIP3 and CMIP4, such as experimental design, especially in improving physical parameterization and the temporal and spatial resolution. The CMIP5 models contain more comprehensive patterns and higher resolution. A key to CMIP5′s usefulness is that all model output conforms to community standards and is placed in an archive that appears to users as a single unified database. This makes analysis of the multi model ensemble nearly as easy as analysis of a single model. So many studies choose CMIP5 models to analyze climate change. Torres et al. [28
] chose several GCMs and forcing scenarios from CMIP3 to CMIP5 to identify South America regions where climate change could be more pronounced in a warmer climate. Basheer et al. [29
] used four GCMs from the CMIP5 to assess the impacts of climate change on the streamflow in the Dinder River basin and found that the predicted climate change is likely to affect ecosystems positively and promote the ecological restoration for the habitats. Sun et al. [30
] evaluated 14 global climate models in the CMIP5 to capture the extreme climate events and the agricultural climate indices over China. Liu et al. [18
] studied the risk-based assessment of changes in global drought and the impact of severe drought on populations under CMIP5 warming conditions and finally given some information and advice to reduce the future drought risk and impact. Ma et al. [24
] used the CMIP5 to study the trends in the area of arid/humid climate regions of China and identify the regions of arid/humid patterns change over the next 100 years, and found that the humid region would suffered a significant contraction and the arid/humid transition zones may be lead to an expansion. So many previous studies have tested and verified that the CMIP5 models, as important tools on climate change, could well applied to the climate associated impacts research. In this paper, three CMIP5 climate models, such as CNRM-CM5 (CNR), HadGEM2-ES (Had), and MIROC5 (MIR), would be chosen to analyze the drought response to climate change with two Representative Concentration Pathways (RCPs) scenarios, namely, RCP4.5 and RCP8.5.
Quantification of drought is the premise of drought research. Nowadays, a variety of drought indices have been developed [13
] and applied in the fields of meteorology, hydrology, agriculture, and socio-economic. The drought indices include the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI), Keetch–Byram drought index (KBDI), surface water supply index (SWSI), the standardized streamflow index (SSI), Palmer drought severity index (PDSI), crop moisture index (CMI), and vegetation condition index (VCI). Different drought indices play an important role in drought analysis, but there are still some shortcomings and limitations for they were consider different physical mechanism and mathematical model [13
]. Some indices lack the effectiveness of spatial and temporal comparisons, such as the PDSI. While, some indices ignore the effect of evapotranspiration changes caused by the temperature rise, such as the SPI [38
]. The American Meteorological Society [39
] suggests that the time and space processes of supply and demand are the two basic processes that should be included in an objective definition of drought and in the derivation of a drought index. The standardized precipitation evapotranspiration index is one of such drought indicators. SPEI was proposed by Vicente-Serrano et al. [40
] and it has the advantages of the sensitivity to water expenditure in forms of evapotranspiration caused by temperature and the characteristics of multi-time scales like the SPI [42
]. Based on the above advantages, it has been widely used in different countries and regions over the world [8
], showing a good performance on drought analysis. For China, Li et al. [47
] compared the SPEI and the SPI for drought analysis and indicated that the SPEI could better monitor the drought conditions than SPI in months with significant increase of temperature. Shi et al. [48
] showed that the SPEI values effectively reflected the spatial and temporal pattern of drought occurrence in Henan Province. Zhao et al. [49
] indicated that SPEI was suitable for both short- and long-term drought monitoring compared with PDSI and had a good application prospect in China. Various research results have shown that SPEI has the characteristics of simplicity of calculation and consideration of the impact of temperature variability. It is especially suitable for the study of drought under the current global warming.
Given the importance of this issue and the lack of previous studies, the main objectives of this paper are structured as follows: Section 2
provides short descriptions of the study area and the datasets used in the research. This section also presents brief discretions of the used methods. In Section 3
, the future climate changes characteristics of precipitation and temperature in the study area are shown by three different CMIP5 climate models under two emission scenarios (RCP4.5 and 8.5). It also studies the changes of drought tendency and frequency and the differences of drought severity, duration, and intensity historically and in the future. At the end of Section 3
, the study discusses how the precipitation and temperature influences the historical and future drought situations under the climate change. Lastly, Section 4
offers the conclusion of this study.
In the upper and middle reaches of the Huai River Basin, the three CMIP5 models differ in describing the future seasonal and annual precipitation and temperature. The statistical values of MIROC5 are the largest in describing future annual and seasonal precipitation, while the values of CNRM-CM5 and HadGEM2-ES are smaller but closer. Meanwhile, MIROC5 are the biggest for describing the temperature in the future years and seasons, then the second is HadGEM2-ES and the third is CNRM-CM5.
Among the three CMIP5 models, the average precipitation and temperature in future years and four seasons would increase in most periods and scenarios, except that of CNRM-CM5 and HadGEM2-ES in some seasons and scenarios below the historical level. Under the three models, the annual precipitation would increase significantly on the significant level of 0.01 with the M-K test values greater than 2.90 in the future under high concentration emission scenarios. Most of the seasonal precipitation would increase but not in all four seasons. The annual and seasonal temperature of RCP4.5 and 8.5 scenarios under the three models showed an extremely significant warming trend on the significant level of 0.001 with the M-K test values greater than 4.00, especially under the high concentration path. The different changes of precipitation and temperature make the risk of future flood and drought greater.
The general trend of historical drought was wetting between 1960 and 2015, except the flat performance in spring and the arid showing in autumn. The historical frequency of mild drought ranged from 10% to 20% with interdecadal variation. The overall performance of historical total drought (SPEI ≤ −0.5) frequency showed more than 35% in 1960s and declined more than 25% in 1970s–1990s and then dropped to less than 25% when entering the 21st century. The frequency of historical moderate, severe and extreme drought and total drought and the historical annual characteristics of drought severity, drought months, and drought intensity all showed a downward trend. Among them, the historical drought severity and duration peaked in 1966, 1978, and 2001, but the peak value continued to decline.
Three CMIP5 models showed that there are differences in describing drought trends, frequency changes and drought characteristics in the future. Overall, the basin has a trend of drought in the future and the trend is stronger with a higher greenhouse gas emission concentration. The frequency of severe drought may increase in the future, which mainly related to the significant increase of temperature warming. The total drought frequency would increase slightly comparing with the beginning of the 21st century and return to more than 35% at the end of the 21st century, especially under RCP8.5 scenario. The drought characteristic values in the future show an upward trend but they are differences in the increase range under different models with RCP4.5 and 8.5 scenarios. On the whole, the drought characteristics of the basin in the future are more serious than the historical period, and the annual drought severity is greater, the drought duration is longer, the drought intensity and the maximum drought intensity are bigger. The maximum value of future annual drought severity and duration could reach 16.85 and 11 months under MIROC5 RCP8.5 scenarios, respectively, while, those of that were 12.40 and 7 months in the historical periods, respectively. In view of the serious and extreme drought characteristics of the basin under future climate change, it is necessary to strengthen the response research to drought risk.
Lower precipitation and higher temperature are the main factors contributing to the formation of drought events. Lower precipitation with lower temperature is generally weak in drought severity. If the precipitation increases but the temperature increases relatively larger, it should consider the change of evapotranspiration caused by the increase of temperature, which is more serious than that caused by the increase of precipitation but the small increase of temperature in the same period. Considering that the significant trend of precipitation increase in the future is lower than that of temperature rise, the influence of temperature should not be neglected in future drought research.
Drought under climate change needs continuous research and it should pay much attention to the precision test of climate model selection. The statistical downscaling or physical downscaling should be strengthened to obtain the higher spatial and temporal resolution values of climatic element for enhancing the credibility of drought research under the influence of climate change.
The results would be beneficial for the study of regional drought response to different climate models and emission scenarios and of great significance to regional water resources strategic planning, drought disaster prevention and control, and agricultural development planning.