water Article Cryosphere Water Resources Simulation and Service Function Evaluation in the Shiyang River Basin of Northwest China Kailu Li 1,2, Rensheng Chen 1,* and Guohua Liu 1,2 1 Qilian Alpine Ecology and Hydrology Research Station, Key Laboratory of Ecohydrology of Inland River Basin, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China; [email protected] (K.L.); [email protected] (G.L.) 2 University of Chinese Academy of Sciences, Beijing 100049, China * Correspondence: [email protected] Abstract: Water is the most critical factor that restricts the economic and social development of arid regions. It is urgent to understand the impact on cryospheric changes of water resources in arid regions in western China under the background of global warming. A cryospheric basin hydrological model (CBHM) was used to simulate the runoff, especially for glaciers and snowmelt water supply, in the Shiyang River Basin (SRB). A cryosphere water resources service function model was proposed to evaluate the value of cryosphere water resources. The annual average temperature increased significantly (p > 0.05) from 1961 to 2016. The runoff of glacier and snowmelt water in the SRB decreased significantly. This reduction undoubtedly greatly weakens the runoff regulation function. The calculation and value evaluation of the amount of water resources in the cryosphere of Shiyang River Basin is helpful to the government for adjusting water structure to realize sustainable development. Keywords: climate change; the Shiyang River Basin; glacial runoff; snowmelt water; cryosphere; value evaluation Citation: Li, K.; Chen, R.; Liu, G. Cryosphere Water Resources Simulation and Service Function 1. Introduction Evaluation in the Shiyang River Basin Cryosphere science is an emerging science. The cryosphere elements consist of glacial of Northwest China. Water 2021, 13, ice, sea ice, ice shelves, ice caps, continental glaciers, valley glaciers, permafrost, as well 114. https://doi.org/10.3390/ as snow and ice in rivers and lakes [1]. Studies on the cryosphere have accelerated since w13020114 1972 when, at the Stockholm Human Environment Conference, the World Meteorologi- Received: 10 December 2020 cal Organization (WMO) proposed the cryosphere as a fifth earth sphere alongside the Accepted: 29 December 2020 atmosphere, hydrosphere, lithosphere, and biosphere [2]. Subsequently, the World Cli- Published: 6 January 2021 mate Research Programmer (WCRP) launched its core “climate and cryosphere” (CliC) plans in 2000. Then, the International Union of Geodesy and Geophysics (IUGG) made Publisher’s Note: MDPI stays neu- the decision to add the International Cryospheric Science Association (IACS) as a new tral with regard to jurisdictional clai- association in 2007. Since the start of the twenty-first century, cryosphere research has seen ms in published maps and institutio- unprecedented development around the world [2]. The Fifth Assessment Report of the nal affiliations. Intergovernmental Panel on Climate Change (IPCC) confirmed the fact of global warming in the past 100 years and pointed out that the impact of human activities has been the main cause of climate warming since the mid-20th century [3]. Much of this frozen world, the cryosphere, has been melting as a result of global warming [1]. In the western cold regions Copyright: © 2021 by the authors. Li- of China (WCRC), many changes have taken place in the cryosphere. The glacier area censee MDPI, Basel, Switzerland. has decreased by 12.9% from 1960 (59,425 km2) to 2012 (51,766 km2)[4,5]. The permafrost This article is an open access article has experienced widespread degradation [6]. Snow cover has shown a small increase distributed under the terms and con- ditions of the Creative Commons At- trend in the WCRC between 1951 and 1997 [7]. These changes will definitely affect the tribution (CC BY) license (https:// water cycle and yearly runoff variation in the cold alpine watershed [8–12]. An increase or creativecommons.org/licenses/by/ decrease in river basin runoff will have an important impact on river basin water resources 4.0/). planning, management, and sustainable use. With the proposal and development of the Water 2021, 13, 114. https://doi.org/10.3390/w13020114 https://www.mdpi.com/journal/water Water 2021, 13, 114 2 of 22 concept of cryosphere service function [13–16], and the establishment of a scientific system of cryospheric science, cryospheric changes and their impacts have received increasing concern [2]. The impact of changes in the cryosphere on the socioeconomic field is now a research hotspot. Its research route is change, impact, adaptation, and service. Quantifying the effect of cryospheric changes on runoff in the WCRC has been the basis of research. Much work has been performed on climate and streamflow changes for individual basins in the WCRC. Chen et al. [17] investigated the hydrological response to climate change in the Tarim River Basin. In the same year, Li et al. [18] analyzed the influence of climatic change on the flow over the upper Hei River Basin (UHR). Later, Ma et al. [19] studied eight catchments in the Shiyang River Basin (SRB) and investigated changes in annual streamflow in the WCRC. Wang et al. [20] investigated the effects of climate change on streamflow of the Xiying and Zamu rivers in the SRB, based on the Soil and Water Assessment Tool (SWAT). These studies lack an analysis of climate change on glacial and snowmelt water. Melt modeling is a crucial element in any attempt to predict runoff from snow-covered or glacierized areas, as well as to assess changes in the cryosphere associated with climate change [21]. Singh et al. [22] developed a conceptual snowmelt model (SNOWMOD) based on the temperature index model and applied it to the study of the contribution of glaciers and snowmelt to the runoff in the Himalayas. Konz et al. [23] used the TAC (D) model to simulate runoff in a poorly gauged, highly glacierized Himalayan head- water. Chen et al. [24] constructed several models to simulate Koxkar glacial meltwater runoff. Zhao et al. [25] coupled energy balance and a mass balance algorithm to the variable infiltration capacity (VIC) model, and used it to simulate the glacial runoff in Aksu River Basin. Luo et al. [26] coupled the glacier module with the SWAT model to simulate the glacier runoff process in the Manas River Basin in the Tianshan Mountains. Model simulation is the main method for a comprehensive analysis of watershed hy- drological elements. Distributed hydrological model coupled with glaciers, snow cover, and frozen soil modules can output these results. Creatively, Chen et al. [27] proposed a new distributed cryospheric basin hydrological model (CBHM) to evaluate the effects of cryospheric changes on streamflow in the UHR, and they studied and discussed the comprehensive effects of cryospheric changes on river runoff, including glaciers, snow cover, and permafrost, in the past and future. The study of cryosphere service (CS) function and its value evaluation is still in the infancy stage. Xiao et al. [28] defined CS as the benefit that the cryosphere provides to human society, and classified the different services of CS as supply, accommodation, social culture, and living environment service. Later, some scholars [13,29–32] also studied the service function of the cryosphere. However, these studies were mainly theoretical studies on CS and lacked further practical research. Cryosphere water resources service (CWRS) is the most significant CS to directly affect human societies [30], which is the important breakthrough of the research of service function in cryosphere [33]. We aim to make a breakthrough in this area. A CBHM applied to the upper Hei River Basin has achieved very good results, which have formed the basis for research on CWRS. However, research on CWRS cannot only involve a small watershed. Whether the model can be applied in more watersheds and a larger scale is a problem that needs to be solved. Further studies are still necessary. The purpose of this paper is to apply a CBHM to the scale of a water system. Furthermore, we aim to propose an evaluation system of CWRS function and also study the current status of CWRS functions. In this study, we applied a CBHM to seven catchments in the SRB, an important arid region in northwest China. The monthly runoff and its components were simulated from 1961 to 2016. Using the model output of cryosphere water resources and the socioeconomic data, we evaluated and divided the functions of CWRS in the study area. Our research expanded the research scale from a single watershed to the scale of a water system containing multiple watersheds and provided ideas and methods for studying the service function of the cryosphere water resources. Water 2021, 13, 114 3 of 22 2. Study Area and Methods 2.1. Study Area The Shiyang River Basin is located in the east part of the Hexi Corridor in Gansu Province in northwest China [19]. It is on the west of the Wushaoling Mountains and north of the Qilian Mountains at longitude of 100◦570–104◦120 E and latitude of 37◦020–39◦170 N, occupying an area of 41,600 km2 (Figure1). The administrative divisions of the watershed include the four prefecture-level cities of Jinchang, Wuwei, Zhangye, and Baiyin, and nine counties of Liangzhou, Gulang, Minqin, Tianzhu, Yongchang, Jinchuan, Sunan, Shandan, and Jintai. The Shiyang River Basin is one of the three inland river basins of the Hexi Corridor, and the headwater rivers from east to west are the Dajing, Gulang, Huangyang, Zamu, Jinta, Xiying, Dongda, and Xida Rivers. The flow characteristics of the river and the control station information are shown in Table1. The sources of river supply are atmospheric precipitation in mountainous areas and melting snow and ice in the high mountains. The mean annual runoff is 1.50 billion m3.