Hydrological response to changing climate: a case study of large watershed, Xianning, Hubei, China

ABSTRACT This study is composed of assessment of air temperature, rainfall, available water reservoir, and runoff potential. The analysis of air temperature and rainfall (1996–2010) in the Xianning watershed, which was composed of Tongcheng, Chibi, and Jiayu small catchment areas was carried out and various extreme events (for example, floods in Yangtze river) were recorded. The climatic conditions of the watershed were evaluated over a period and the impacts of climatic change were investigated. Then, a forecasting model was developed for the future climatic changes (up to 2025) and the hydrological response due to these climatic changes in the study area was discussed. The results showed increasing temperature and decreasing rainfall, and that the changing climate mostly drifted during the 1990 s and onwards. It is foreseen that the natural extreme events have shifted with the seasons and there is an increase in the frequency and intensity of extreme. The future planning for water resources ought to consider the probable environmental change scenario, which entails an indulgence of both sensitivities to change and recent changeability over time.


Introduction
Climate changeability impacts are potential concerns nowadays and the climate system is varying faster than the natural patterns. Climate change impacts the environmental, ecological, and hydrological courses at global, regional, and local levels. These impacts can interrupt the structure and effectiveness of the ecosystem, increase natural disturbances, and change the distribution of water resources and vegetation patterns. Climate change has a substantial impact on the hydrological response that has then affected the available water resources (Zhang et al., 2011). The variation in precipitation, droughts, runoff, and evapotranspiration is because of climate change (Dai et al., 2018). The Intergovernmental Panel on Climate Change (IPCC) has studied that watersheds are badly affected because of the changing pattern of temperature and precipitation (Simonovic, 2017). In a watershed, the streamflow fluctuates non-linearly with changing in precipitation (Zhang et al., 2019).
In dry areas, an increase in temperature associated with an increase in evaporation and transpiration which can cause a big variation of runoff and streamflow, however in humid areas, any change in precipitation causes a large variation of streamflow . In recent decades, the significant impact of climate change on water resources and hydrology has attained great attention through several studies in many regions all around the world. Therefore, a hydrological response analysis is very important to evaluate the sensitivity of a watershed to climate change circumstances and to develop better water management structures and climate change adaption tactics. Lirong and Jianyun (2012) investigated hydrological response to climate change in Beijiang River Basin and their results indicate that when precipitation keeps unchanging, temperature increase would increase average annual evaporation and potential evaporation and decrease water yield. Zaheer et al. (2016) reported the hydrological alterations and precipitation assessment within the watershed and to investigate the watershed's behavior and structural disturbance from various morphological parameters for example, runoff, stream density, bifurcation ration, and stream order.
Many research studies on precipitation changes were done at country or regional levels because of the climate changes at regional level (Brunetti et al., 2004;Khan & Zaheer, 2018;Thompson, 1999) and the analysis of long-term simulated precipitation data by climate models (Coppola & Giorgi, 2010;Gregory & Mitchell, 1995). Water resources will be improved in some regions of the world and on the other hand, will be degraded in some regions of the world. The ecological, environmental, and hydrological response is more sensitive to anthropogenic climate change than natural climate variability. The climate change variations indicated the decreased water balance components in the Heeia Watershed in Hawaii of the USA (Leta et al., 2016). The climate change significantly impacted the watershed runoff and hydrological processes in the Ipswich Watershed in Massachusetts of USA and adaptation strategies were recommended to ease climate effects and increase watershed's resilience (Dudula & Randhir, 2016). Ahmad et al. (2016) investigated water resources management about environmental changes in the Himalayan watershed region. Xu et al. (2019) reported that the climate change impacts involving temperature and precipitation disturbances at the watershed scale and indicated that streamflow changes and fluvial flood risk in a mixed-use watershed of Michigan of USA. PuPumo et al. (2017) pointed out that climate change significantly affected the hydrological dynamics and processes in the Eldon River Basin in Oklahoma of the USA. Napoli et al. (2017) presented the climate change played a significant role in hydrological dynamics and runoff changes in the Elsa River Basin in Italy there was an increase of freshwater resources under warmer temperatures and increased rainfalls because of the climate change impacts in the Athabasca River Basin in Alberta, Canada (Shrestha et al., 2017). The wetland's hydrological dynamics and associated services of seasonal contribution, flood mitigation, and water storage were influenced by the climate change in two isolated wetlands and two riparian wetlands in the Becancour River Watershed in Quebec of Canada (Fossey & Rousseau, 2016b).
The impacts of climate change on the hydrological dynamics and relevant hydrological response of the watersheds were studied in China. Q. Zhu et al. (2012) assessed climate change impacts on hydrological response and showed that the water resources would improve in northern China and decline in southern China under climate change scenarios). Y. Zhu et al. (2016) evaluated the impacts of climate change on water resources and extreme flows using different models, scenarios, and simulations. Their results indicated that the reduction of water resources and the increase of extreme flood events due to increased rainfall in the Yellow River Basin in Northern China. Climate change showed a considerable impact on water availability leading to the reduction of water response in the North China Plain in Northern China . Zhang et al. (2017) found that the climate change was the considerable factor for runoff variability in the Haihe River Basin in Northern China and was much contributed to runoff changes as compared to other factors in the Yanhe River Basin in Northern China (Wu et al., 2017). The increased temperature and changes in precipitation pattern leading to an increasing trend of extreme events like floods and droughts in the Eastern Monsoon Region of China . Environmental change can adjust the risk of hydrological extremes at regional scales (Alodah & Seidou, 2019) even though developed basins with a dense population are highly vulnerable to hydrological extremes.
The rainfall variability due to climate change would lead to frequent and intense extreme events like floods and droughts. The rapid temperature increase would lead to the rapid melting of glaciers and influence the freshwater sources at large scale and would lead to flooding from glacial lakes in the upper reaches of the Yangtze River and lower volume of water in the Yangtze's downstream areas. The main objective of this study was to evaluate the precipitation pattern and temperature variability by using Statistical Package (SPSS) and Minitab software to analyze the data and run the regression analyses to get the bestfitted results. The climatic conditions of the Xianning watershed in the Hubei province of China were evaluated over a period and the impacts of climatic change were investigated and a forecasting model was developed for the future climatic changes (up to 2025).

Study area
This study was conducted at Xianning in southeast Hubei province, China, covering about 1501 km 2 . Xianning is about 50 km away from the provincial capital of Wuhan. It is characterized by a typical subtropical warm and humid climate, with an annual mean temperature of 16.8 °C and a frost-free period of 254 days. The mean annual precipitation is about 1570 mm , and the rainfall concentrated between April and July accounts for about 50% of annual precipitation. The terrain of Xianning is composed of two parts: the low mountainous area in the southeast part, accounting for 23% of the total area; and the hilly area in the northwest, accounting for 77% of the total area. The elevation ranges from 18 m above sea level (ASL) in the northwest to 954 m (ASL) in the southeast.

Data collection
The annual air temperature and rainfall data (1996--2010) of the three areas (Tongcheng, Chibi, and Jiayu) of Xianning were collected from the Xianning Meteorological Bureau. The annual air temperature and rainfall of Xianning were calculated from the average mean values of these three regions of Xianning. The climatic disaster events and their impacts data  were collected from the Xianning Civil Affairs Bureau. The water resources data (2001)(2002)(2003)(2004)(2005) was collected from the Xianning Water Conservancy Website.

Results and discussion
This conducted study echoed a trend of gradual impact of climate change in the Xianning watershed. This was evident from the changing variation trends of the annual temperature and rainfall of this region. The temperature trend of the three regions (Tongcheng, Chibi, and Jiayu) and their average mean temperature for the Xianning watershed area is shown in Figure 1. There is an overall increasing trend of the annual temperatures in the Xianning watershed region.
The rainfall pattern of the three regions (Tongcheng, Chibi, and Jiayu) and their average mean rainfall for the Xianning watershed area is shown in Figure 2. There is an irregular trend in the rainfall pattern till 2002 (involving three extreme rainfall years of 1996, 2000, and 2002), which suddenly shifts to a decreasing trend from 2003 to 2008 in the Xianning watershed region. Furthermore, it is noteworthy that an extreme rainfall event occurs at an interval of every two or three years during the period 1996-2003. After that, the rainfall decreased during the period 2003-2008, which may result in a depression of the water resource recharge in the region.
There is a significant increment in temperatures under three projected scenarios graphically represented in Figure 3(a-c) for regions of Xianning and in Figure 3(d) for the overall Xianning watershed region. The significant temperature rising until 2025 is clearly shown in Figure 3(a-d).
The trend of annual precipitation under three projected scenarios is graphically represented in Figure 4 (a-c) for regions of Xianning and in Figure 4(d) for the overall Xianning watershed region. The irregular and decreasing trends of rainfall till 2025 are shown in Figure 4(a-d).
The declining trend of rainfall in this area can be noticed by the gradual lowering of rainfall in the targeted regions of Xianning watershed. This clearly explains the climate change and its future impacts involving extreme climatic events and other disasters extrapolated through these findings. Rainfall was declining with time but as per the available data, the intensity of rainfall is unusual during the past five years. This is leading to consequent natural disasters such as an increase in flood frequency and enhanced losses in recent times. The most frequent natural disaster encountered in Xianning watershed is flooded, followed by frost and drought spells. These extreme climatic events occurred consistently and seem to increase in the last decades. The intensity of the extreme climatic events increased with the increase in losses from 1995. The 50-year (-1969-2009) statistics of climatic disasters and their impacts in the Xianning region are shown in Table 1.
The overview of the water resources from 2001 to 2005 in the Xianning watershed is shown in Table 2. The results of this study showed that climate change    involving temperature and rainfall variations significantly impacts the water resources in this region.
Although the subject tenure is less than required, it potentially discovers the rate of rainfall during the defined period and storage of reservoirs in million cubic meters (m 3 ). The average rainfall in the region describes the storage power in the reservoirs. In the year 2002, a clear expression of highest rainfall is given but the storage capacity was almost 30% less than the year 2003 with a comparatively less average rainfall of 102.8 cubic meters. The average at three regions depicts the rising temperature either directly or indirectly resulting from the industrial emissions and deforestation practices (Yedla & Park, 2017). A similar result was also found by Su-Qin et al. (2013) indicated that a clear increasing trend of annual mean temperature in Central China during 1961-2010. The increasing rate of annual mean temperature reached 0.15°C per decade, which is lower than the mean increasing rate in the whole of China (0.23°C per decade from 1951 to 2009).
The extreme hot atmosphere was specifically influenced by the amazing concentration and western augmentation of the subtropical high weight in the western Pacific Ocean, which was well connected with the worldwide temperature alteration (Yang & Li, 2005). Additionally, a few studies proposed a propensity of this kind of great temperature, regarding recurrence and the extent of events, being either the same or higher later. The escalating rate in yearly mean temperature amid 1961-2010 was extensive in eastern Hubei and northeastern Hunan, at the rate of 0.21° to 0.32°C per decade. The increase of temperature in Jiayu is significant in the Xianning region as the data from the past two decades explains the rise in temperature. The impact of natural disasters entailed a significant increase in intensity and a decrease in the frequency of the events (Meng et al., 2015). This may be an impact on the region due to global warming and climate change.
The understanding of human-climate-environment interactions is important for the assessment of ecosystems' vulnerability to future climate change impacts (McGregor et al., 2009). The three discrete adaptation approaches are social vulnerability approaches focused to tackle social issues, resilience approaches focused to enhance the resilience of systems and targeted adaptation approaches focused on actions for dealing with climate change risks (Nelson & Anderies, 2009). There is a relationship between domains of resilience, vulnerability, and adaptation within the human dimensions of climate change (Janssen et al., 2006).
The monitoring and warning systems can be improved as main efforts for adaptation to climate extremes and reduction of disaster impacts. Better management practices are needed for adaptation to and mitigation of climate impacts on watershed such as water runoff variations. Climate change is profoundly impacting the hydrological response in the watershed. The global warming involves the increasing temperatures and their effects.
Our study supports the global warming theory as the temperatures are increasing in our study area. The increasing temperatures would lead to the rapid melting of glaciers which can cause flooding in some areas and would increase evaporation rates which can lead to a shortage of available water resources. The increasing temperatures and decreasing rainfall trends would lead to a shortage of water resources in this region. Climate change would also increase the frequency and intensity of extreme climatic events such as floods, droughts, heatwaves, cold epochs, etc. The extreme climatic events inflict significant damages and losses to the humans, ecosystems, and the environment. Based on this study, for future research, to envisage the hydrological changeability because of the land-use, as there are numerous inconsistencies, accompanying with future climate change systems.

Conclusion
Climate change impacts have been observed in the study region. The following conclusions are drawn from this study.
(1) Increased in annual mean temperatures and decreased in annual total rainfall are consequently leading to more frequent and intense climatic disasters in the study region. These extreme climatic events occurred consistently and seem to increase in the last decades.
(2) The analysis describes that the micro impact on the region which is certainly affecting the climate of the Xianning and whole area is under the threat of amplified natural disasters and losses risk. (3) The development of green infrastructure would support flood risk mitigation and climate extremes alleviation. The complete evaluation of temperature and precipitation, water storage volume, and flood risk analysis for different scales and periods would support decisionmaking on climate change adaptation and mitigation and water resources management. (4) Based on the assessment of this study, it is concluded that the available data for changing climate trends and its impacts in this region is very limited. Therefore, to improve the environment of this region and reduce climatic disasters, urgent action is required.