Glacier area change and its impact on runoff in the Manas River Basin,Northwest China from 2000 to 2020

Understanding the distribution and dynamics of glaciers is of great significance to the management and allocation of regional water resources and socio-economic development in arid regions of Northwest China.In this study,based on 36 Landsat images,we extracted the glacier boundaries in the Manas River Basin,Northwest China from 2000 to 2020 using eCognition combined with band operation,GIS(geographic information system)spatial overlay techniques,and manual visual interpretation.We further analyzed the distribution and variation characteristics of glacier area,and simulated glacial runoff using a distributed degree-day model to explore the regulation of runoff recharge.The results showed that glacier area in the Manas River Basin as a whole showed a downward trend over the past 21 a,with a decrease of 10.86%and an average change rate of–0.54%/a.With the increase in glacier scale,the number of smaller glaciers decreased exponentially,and the number and area of larger glaciers were relatively stable.Glacier area showed a normal distribution trend of increasing first and then decreasing with elevation.About 97.92%of glaciers were distributed at 3700–4800 m,and 48.11%of glaciers were observed on the northern and northeastern slopes.The retreat rate of glaciers was the fastest(68.82%)at elevations below 3800 m.There was a clear rise in elevation at the end of glaciers.Glaciers at different slope directions showed a rapid melting trend from the western slope to the southern slope then to the northern slope.Glacial runoff in the basin showed a fluctuating upward trend in the past 21 a,with an increase rate of 0.03×10^(8) m^(3)/a.The average annual glacial runoff was 4.80×10^(8) m^(3),of which 33.31%was distributed in the ablation season(June–September).The average annual contribution rate of glacial meltwater to river runoff was 35.40%,and glacial runoff accounted for 45.37%of the total runoff during the ablation season.In addition,precipitation and glacial runoff had complementary regulation patterns for river runoff.The findings can provide a scientific basis for water resource management in the Manas River Basin and other similar arid inland river basins.

Surface runoff processes and sustainable utilization of water resources in Manas River Basin, Xinjiang, China

Water is the important resource to guarantee the existence and development of oases in arid areas. To improve the utilization efficiency of water resources in Manas River Basin, this paper investigated the trends and periods of runoff based on the runoff and climate data for the past 50 years. Subsequently, with the socioeconomic and water resources data, we studied a comprehensive evaluation on the water security in this area. The results indicated that the stream flows in the three hydrological stations of Hongshanzui, Kensiwat and Bajiahu have sig- nificantly increased and undergone abrupt changes, with periods of 18 and 20 years. According to assessment, water security in the Manas River Basin was at an unsafe level in 2008. In criterion layer, the ecological security index and the index of supply-demand situation are both at the relatively secure level; the quantity index and so- cioeconomic index of water resources are at the unsafe level and basic security level, respectively. Therefore, in order to achieve sustainable economic and social development within the Manas River Basin, it is vital to take a series of effective measures to improve the status of water security.

The Effect of Extreme Climatic Events on Extreme Runoff in the Past 50 Years in the Manas River Basin, Xinjiang, China

To analyze extreme climatic change features and effects on runoff in the Manas River basin, Xinjiang, data were collected including daily mean temperature, daily highest and lowest temperatures, and daily precipitation from six meteorological stations in the Manas River basin as well as daily runoff data from the Kensiwate hydrologic stations during 1960-2010. By adopting the threshold value of extreme climatic events defined by ET ALDDMI and with the aid of nonparametric statistical tests, Pearson III methods, and others, the effect of extreme climatic events on extreme runoff in the past 50 years in the Manas River basin, Xinjiang, was analyzed. The results showed that in the past 50 years, 1) extreme warming events (annual extreme maximum temperature, warm-day and warm-night index) have risen significantly (P < 0.05). Among these the warm-day and warm-night indices decreased abruptly in 2001 and 1996, respectively. With respect to extreme cold events (annual extreme minimum temperature, cold-day and cold-night indices), the extreme minimum temperature was high after 1976, and the cold-day index weakened significantly, similar to the cold-night index. 2) Except for the continuous drought days (CDD), the other five indices of extreme precipitation events appeared to trend upward, with an abrupt change around 1993. 3) Flood events in 1990, mostly in summer, accounted for 42.9% of the total number of floods since 1960. Floods increased mainly because extremely high summer temperatures increased snowmelt, increasing inflow to the rivers, which combined with more precipitation to cause the increase in summer peak flood discharge.

Transformation of surface water and groundwater and water balance in the agricultural irrigation area of the Manas River Basin,China

Calculation of the water balance is very important to relieve the pressure on water resources in arid agricultural irrigation areas.This research focused on irrigation water balance calculations in the Manas River Basin of the southern margin of the Junggar Basin of China,and aimed to analyze the groundwater level dynamic trend and response characteristics of the basin water cycle under water-saving irrigation measures.The surface water and groundwater coupling model of MIKE 11-Visual MODFLOW was used to simulate rainfall runoff in mountainous areas,and quantify the contribution of water balance components in the plain irrigation area.Convergence of the delayed watershed in the mountain area was obvious,and when the river runoff exceeded 200 m^(3)/s,the error in the runoff simulation was large.The water balance in the plain agricultural irrigation area was in a negative equilibrium state,and the difference between recharge and discharge was−2.65 billion m^(3).The evapotranspiration was 24.49 billion m^(3) under drip irrigation,accounting for only approximately 51%of the total discharge.The lateral discharge of the unsaturated and saturated aquifers was 15.38 billion m^(3),accounting for approximately 32%of the total discharge.The main reason for the groundwater decline in the irrigation area was closely related to the extraction of groundwater,because the amount of recharge and discharge in the natural state was approximately identical.The MIKE 11-Visual MODFLOW model produced accurate results,and the research method provided a new exploration technique to quantify the effect of water supply mode on the groundwater table.The model is suitable for the management of water resources in arid areas.

Land use change characteristics affected by water saving practices in Manas River Basin,China using Landsat satellite images

The characteristics and influencing factors of land use change under arid conditions were studied in the Manas River Basin in Xinjiang Region,Northwest China.Landsat satellite images acquired in 1976,1990,2000,2010 and 2015 over the study area were used as basic data.Land use change,the rate of change of land use,land use transfer and other aspects revealed the characteristics of land use change and related factors as influenced by water conditions in the basin.The results showed that:(1)Over nearly 50 years,land reclamation in the Manas River Basin resulted in the rapid expansion of an artificial oasis area,and promoted the process of‘oasis urbanization’,and accelerated the development of the river basin economy.(2)In 2000,the popularization of drip irrigation under mulch technology led to the rapid growth of cultivated land and development land in the watershed.Meanwhile,the water table declined in the desert area of the lower reaches of the river basin,and the area occupied by sparse shrub forest and grassland decreased.(3)Before popularization of water-saving technology,woodland,grassland and development land transformed to cultivated land in the amounts of 93.46 km^(2),2542.93 km^(2) and 137.53 km^(2),respectively,and woodland transformed in the amount of 189.64 km^(2).After water-saving technology was popularized,woodland,grassland and development land were transformed into cultivated land in the amounts of 567.41 km^(2),1756.2 km^(2) and 37.36 km^(2),respectively.(4)The popularization of water-saving technology made the dynamic degree of cultivated land and development land more active,and further increased landscape fragmentation and landscape heterogeneity.The level of urbanization development,the level of economic development and the dry humidity of the basin became the main factors affecting the change of land use in the basin.

Effects of drip irrigation on components of water cycle in arid inland areas: A case study of Manas river basin in northwestern China

Compared to either drip irrigation or mulching with plastic film,the two methods together can reduce water requirements of crops grown in arid areas by more than 30%.Such a combination deployed on a large scale(1)reduced the loss of soil water by 31.8%compared to that from drip irrigation alone;(2)narrowed the range of annual evapotranspiration from 1582.4-1780.3 mm,which is average for the basin,to 222.2-294.8 mm;and(3)increased the overall humidity in the central plain of the basin.However,the surrounding regions in which drip irrigation is not combined with mulching are getting more arid;thus,as a result of the water-saving technology,both oases and the desertification of the river basin are increasing at the same time.The results of the study further the understanding of the effects of drip irrigation combined with mulching on water cycles in the basin of the Manas river and suggest ways to protect the ecology and the environment of the basin.

Response of groundwater to the process of reservoirs group regulation and storage in Manas River Basin in Xinjiang

Reservoir regulation and storage is the main approach to alleviate the water pressure caused by the uneven spatial and temporal distribution of surface water resources in arid areas of northwest China.While the regulation and storage of the reservoir affect the conditions of recharge and discharge of groundwater,the process of regional surface-groundwater transformation tends to be complicated.The Manas River basin that lies on the northern slope of Tianshan Mountain in Northwest China was taken in this study as a case.A numerical model of groundwater in basin plain area was established,and the influence of reservoir regulation on groundwater level was studied.The results showed that the total recharge of groundwater in the study area was 75.539 million m3,the total discharge of groundwater was 82.66 million m3,and the groundwater in the study area was in a negative equilibrium state,with a difference of-69.27 million m3.The water balance method was used to verify the comparison.The total recharge of groundwater was 74.34 million m3,the total discharge of groundwater was 80.726 million m3,and the calculation result of the numerical simulation of the supplementary displacement was 63.82 million m3,basically consistent with the calculation result of the water balance method.The reservoir storage method has obvious changes to the groundwater level around the reservoir.The simulation results of groundwater numerical model showed that when the reservoir was in normal operation,the leakage of the reservoir was 27.35 million m3;when the reservoir was operated at low water level,the leakage of the reservoir was the smallest,13.47 million m3.The reservoir has the largest amount of leakage of 41.85 million m3 when operated at water storage level.When the reservoir was operated at the lowest water level,the groundwater level around the reservoir was declining compare to the normal operating water level.The maximum drop of the groundwater observation well was 2.1 m,and the maximum monthly average was 0.99 m.When the reservoir was operating at the normal water storage level,the water level of the groundwater around the reservoir has increased compare to the normal operating water level.The maximum increase of the groundwater observation well was 1.5 m,and the maximum monthly average increase was 0.78 m.The influence of the reservoir on the groundwater level was 2000 m upstream and 12000 m downstream.The research conclusions can provide a scientific reference for the development,utilization and management of regional groundwater.

Simulation and construction of the glacier mass balance in the Manas River Basin,Tianshan,China from 2000 to 2016

The glacier mass balance(GMB)is an important link between climate and water resources and has remarkable regulatory functions in river runoff.To simulate changes of the GMB and to analyze the recharge rates of glacier meltwater to runoff in the Manas River Basin(MRB)during 2000-2016,MOD11C3,TRMM 3B43 and other multi-source remote sensing data were used to drive the degree-day model.The results showed that:(1)the accuracy of the remote sensing meteorological data can be corrected effectively by constructing the temperature and precipitation inversion models,and the characteristics of glacial climate can be finely described through downscaling.The average annual temperature was-7.57°C and the annual precipitation was 410.71 mm in the glacier area of the MRB.The zone at an altitude of about 4200 m was a severe climate change zone,and above and below that zone,the temperature drop rates were-0.03°C/100 m and-0.57°C/100 m,respectively,while precipitation gradients were-2.66 mm/100 m and 4.89 mm/100 m,respectively.(2)The overall GMB was negative with a cumulative GMB of up to-9811.19 mm w.e.and the average annual GMB fluctuated between-464.85 and-632.19 mm w.e.Besides,the glacier melted slowly during 2000-2002 and 2008-2010,but rapidly for 2002-2008 and 2010-2016,while the most serious loss of the glacier occurred in 2005-2009.Moreover,the vertical changes of the GMB increased at 244.83 mm w.e./100 m in the ablation zone but only at 18.77 mm w.e./100 m in the accumulation zone.(3)The intraannual runoff strongly responded to the change of the GMB especially in July and August when the loss of the GMB accounted for 75.4%of the annual loss,and when runoff accounted for 55.1%of the annual total.Due to differences in the annual precipitation and snow meltwater outside the glacier,the interannual glacier meltwater recharge rates fluctuated between 19%and 31%.The recharge rate of glacier meltwater to runoff in the MRB was close to that for other basins in the Tianshan Mountains,which may be used as a basis to confirm the reliability of the estimated GMB results.Furthermore,based on the present findings,it is recommended that the research community pursue studies on the GMB in other alpine river basins.

Land use/cover and landscape pattern changes in Manas River Basin based on remote sensing

Large-scale water and soil development in inland river basins in arid areas has made changes in landscape composition and structure,threatening the ecological balance.In order to study the trend of land use/cover and landscape pattern change and its relationship with water resources utilization in Manas River Basin,the land-use data of five periods in 1976,1990,2000,2010 and 2015 were analyzed.The results showed that:(1)During 1976-2015,farmland and construction land continuously increased,forest land and grassland continuously decreased,the water area initially reduced and then increased,the area of saline-alkali land initially increased and then reduced,the overall trend of unused land and the sandy area was decreasing and the area of different time periods is floating.The areas of land-use types either increased or decreased.This indicates that the landscape pattern of the basin changes dramatically,and human activities are the main reasons for this phenomenon;(2)The oasis area increased from 3480.2 km2 in 1976 to 7982.0 km2 in 2015,with an obvious increasing trend.The oasis area clearly increased during 1976-1990,the growth rate was 40.6%,the growth rate of the oasis area was 129.4%.In the last 40 years,the degree of desertification fluctuated and decreased.The increase of the oasis area directly leads to the increase of water resources utilization and aggravates the degree of water resources shortage;(3)The pattern of land-use types showed a non-equilibrium trend.In the region with increasing landscape heterogeneity,the overall landscape pattern was increasingly controlled by the majority of patches.The intensive land management model and drip irrigation under mulch have improved the utilization efficiency of water resources and saved water resources from engineering renovation and irrigation management.

Identifying water vapor sources of precipitation in forest and grassland in the north slope of the Tianshan Mountains,Central Asia

Identifying water vapor sources in the natural vegetation of the Tianshan Mountains is of significant importance for obtaining greater knowledge about the water cycle,forecasting water resource changes,and dealing with the adverse effects of climate change.In this study,we identified water vapor sources of precipitation and evaluated their effects on precipitation stable isotopes in the north slope of the Tianshan Mountains,China.By utilizing the temporal and spatial distributions of precipitation stable isotopes in the forest and grassland regions,Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model,and isotope mass balance model,we obtained the following results.(1)The Eurasia,Black Sea,and Caspian Sea are the major sources of water vapor.(2)The contribution of surface evaporation to precipitation in forests is lower than that in the grasslands(except in spring),while the contribution of plant transpiration to precipitation in forests(5.35%)is higher than that in grasslands(3.79%)in summer.(3)The underlying surface and temperature are the main factors that affect the contribution of recycled water vapor to precipitation;meanwhile,the effects of water vapor sources of precipitation on precipitation stable isotopes are counteracted by other environmental factors.Overall,this work will prove beneficial in quantifying the effect of climate change on local water cycles.

Uncertainties of snow cover extraction caused by the nature of topography and underlying surface

Manas River,the largest inland river to the north of the Tianshan Mountains,provides important water resources for human production and living.The seasonal snow cover and snowmelt play essential roles in the regulation of spring runoff in the Manas River Basin（MRB）.Snow cover is one of the most significant input parameters for obtaining accurate simulations and predictions of spring runoff.Therefore,it is especially important to extract snow-covered area correctly in the MRB.In this study,we qualitatively and quantitatively analyzed the uncertainties of snow cover extraction caused by the terrain factors and land cover types using TM and DEM data,along with the Per（the ratio of the difference between snow-covered area extracted by the Normalized Difference Snow Index（NDSI） method and visual interpretation method to the actual snow-covered area） and roughness.The results indicated that the difference of snow-covered area extracted by the two methods was primarily reflected in the snow boundary and shadowy areas.The value of Per varied significantly in different elevation zones.That is,the value generally presented a normal distribution with the increase of elevation.The peak value of Per occurred in the elevation zone of 3,700–4,200 m.Aspects caused the uncertainties of snow cover extraction with the order of sunny slope〉semi-shady and semi-sunny slope〉shady slope,due to the differences in solar radiation received by each aspect.Regarding the influences of various land cover types on snow cover extraction in the study area,bare rock was more influential on snow cover extraction than grassland.Moreover,shrub had the weakest impact on snow cover extraction.