Zhijun YAO Zhaofei LIU Rui WANG Yili ZHANG Institute of Geographic Sciences and Natural Resources, CAS Sept. 9, 2015 Mammoth Lakes, CA Impacts of Climate Change and Land Use/Land Cover Change on Runoff in the Yarlung Zangbo River Basin, China

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions

Introduction Climate change impacts the hydrological processes and their spatial-temporal pattern. Land use and land cover change (LUCC) accounted for 50% of the reconstructed global runoff trend over the last century. （ NOAA National Climate Data Center ） （ Piao S L, et al, PNAS, 2007 ） 气候变化 带来的径 流变化 土地利用变 化带来的径 流变化 Global Temperature Trends during 1985–2014 Degrees Celsius Per Decade

Introduction Ganges Indus Yalung Zangbo Yangtze Yellow TP The hydrological processes on Tibetan Plateau (TP) are sensitive to climate change, and affect water resources within wide downstream regions. （ Immerzeel, et al, Science, 2010 ） Yalung Zangbo The Yarlung Zangbo River basin (YZRB) is most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.

Introduction To improve water use efficiency, there were many agriculture and water conservancy projects invested by government in the YZRB since the late 1980s. Gradually, the YZRB had become one of regions where land cover changes were most significant on TP. Urban expansionSand-fixation Forestation Hydropower station Reservoir Glacier recession

 Literature review about water resources research in the YZRB Most of studies in the YZRB were focused on spatial and temporal change of single climate and hydrological variables. The researches about climate change and its impacts on runoff in the YZRB has made some progress. However, there have been few studies of effects of LUCC on water availability within the YZRB. Introduction ☆ Limited by the insufficient of long-term and regional observed data Utilization of remote sensing data has drawn wide attention.

Non-parameter statistics—supported by long-term observed data Catchment experiments—generally less than 10 km 2 Hydrological models—uncertainties of model structure parameter  Main methods applied to analyze the impact of climate change and LUCC on hydrological processes ☆ GIS spatial analysis—Easy to perform, Objective results Introduction

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions

Study area —Location Area is about 2.4×10 5 km 2 Up stream: P<300 mm Alpine meadow Midstream: 300 < P<600 mm Alpine grassland Down stream: 600 < P<2000 mm Alpine forest Region 1: Lazi station Region 2: Nugesha station Region 3: Yangcun station Region 4: Nuxia station

Study area —Hydrology  Annual runoff developments were uniform for the 4 hydrological stations  The runoff increased continuously from late 1950s, and reached the peak in Then runoff reduced gradually to the lowest until  1950s and 1980s were the dry periods of the YZRB.  1960s and 1990s were the wet periods of the YZRB. NuxiaYangcunNugesha Lazi Decade Runoff (10 8 m 3 ) NuxiaYangcunNugesha Lazi Year Runoff (10 8 m 3 )

Study area —Hydrology Inter-annual variability characteristic for the runoff in the YZRB  The inter-annual variability for runoff is relative weak compared to other rivers located in China.  The stability of runoff during dry seasons increased gradually from downstream to upstream. Runoff in dry seasons (from November to April) NuxiaYangcunNugesha Lazi Year Runoff (10 8 m 3 )

Study area —Hydrology  Runoff begins to increase from March with temperature rising, recharged by snow melting water and river thawing.  Runoff, consistent with precipitation, concentrates between June and September. Nuxia YangcunNugeshaLazi Month Annual distribution of runoff (%) Runoff Month Annual distribution of precipitation (%) Precipitation

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions

Materials and Methods —Data  Meteorological data Observed precipitation and mean air temperature including monthly, seasonal, and annual series from 15 National Meteorological Observatory Stations between 1974 and 2000  Hydrological data Observed runoff at 4 hydrological stations, including monthly, seasonal, and annual series from 1974 to 2000  Land use and cover data Land use and land cover maps at 1:100,000 from 1980s and 2000, respectively, obtained from remote sensing interpretation by using Landsat/TM data

Materials and Methods —Methods  GIS spatial analysis To build the land cover transition matrix,…  Statistical calculation To assess the significance and magnitude of monotonic trends in hydro-meteorological time series  Water balance equation To evaluate the effects of land cover and climate variables on runoff ☆ It is necessary to investigate impacts of climate change and LUCC on runoff during the frozen period and the melting period, separately.

 Linear trend estimation  Mann-Kendall test Materials and Methods —Methods

 Water balance equation In the hydrologic budget, soil water changes are negligible for long periods. Runoff changes are caused by changes in precipitation, glacier and snow melt and evapotranspiration within the basin. ΔR is total change in runoff; ΔR p is runoff change caused by precipitation, estimated by the product of precipitation change and runoff coefficients ΔR g +ΔR e =ΔR-ΔR P, are runoff changes caused by glacier and snow melt and evapotranspiration Materials and Methods —Methods

Interpolation for annual precipitation Spatial distribution of precipitation in 2000 Change rate of precipitation from 1980s to 2000 Spatial calculation for precipitation layers Multiplied by runoff coefficients ΔR P ΔP PjPj

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions Trends in Climate Variables and Runoff Land Cover Types and Changes Impacts of Climate Change and LUCC on Runoff

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions Trends in Climate Variables and Runoff Land Cover Types and Changes Impacts of Climate Change and LUCC on Runoff

Annual Precipitation (P) for the entire basin showed an increasing trend, mainly caused by an increased monthly P from June to September. The magnitude of most trends of annual and monthly P were greater within Region 2 than in other areas. Annual P showed a decreasing trend within Region 1. P in August showed an increasing trend across all regions. The trends in P were spatially heterogeneous within different regions of the basin. Mann-Kendall test Z statistics Magnitudes of trend The magnitude of wet trend was about 20mm/10yr in the basin. Trends in Climate Variables and Runoff —Precipitation

Annual mean air temperature (MAT) showed a significant increasing trend, especially in Region 3 and 4. The magnitude of warm trends were the largest in January and May, with values over 0.5 ℃ /10yr. The magnitude of warm trend was lowest in February and April with values close to zero. The warm trend was lowest for Region 2 relative to other regions. The magnitude of warm trend was about 0.27 ℃ /10yr in the basin Mann-Kendall test Z statistics Magnitudes of trend Trends in Climate Variables and Runoff —Temperature

Annual “runoff depth (RD)” exhibited increasing trends in all regions, especially within Region 3 and 4. Monthly RD in region 3 showed significant increasing trends during dry seasons. Monthly RD in Region 4 showed increasing trends in most months; Monthly RD in Region 1 and 2 increased only in wet seasons. The largest increase of annual RD was in Region 3, in which the magnitude was about 14mm/10yr. The lowest increase of annual RD was in Region 1, in which the magnitude was about 2mm/10yr. Mann-Kendall test Z statistics Magnitudes of trend Trends in Climate Variables and Runoff —Runoff

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions Trends in Climate Variables and Runoff Land Cover Types and Changes Impacts of Climate Change and LUCC on Runoff

Land use and land cover types (2000) of the YZRB  Glacier and snow cover was estimated as about 7782 km 2 and covered 3.1% the basin area, mainly distributing in Region 3. Region 5 Forest ： 44% Grassland ： 15% Land Cover Types and Changes

 The increased area of forest land and decreased area of grass land were both more than 100 km 2. These two types noticeably changed particularly in Region 3, showed effects of human activity on forests and grassland.  The increases in forest land were caused by forestation projects. Grassland degradation can be due to human factors such as overgrazing… (km 2 ) Land cover change from 1980 to 2000 in different regions of the YZRB

 Glacier and snow cover decreased nearly 40 km 2, especially within Region 3.  Barren land increased by 50 km 2.  The greatest increase of built-up land was in Region 3, which contained the largest numbers of cities and greatest human population. (km 2 ) Land cover change from 1980 to 2000 in different regions of the YZRB

Glacier Water

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions Trends in Climate Variables and Runoff Land Cover Types and Changes Impacts of Climate Change and LUCC on Runoff

Impacts of climate change and LUCC on runoff within the YZRB during the frozen period exerted different effects depending on region :  Climate changes played an important role in affecting runoff in Regions 1 and 2 based on the fact that runoff was positively and negatively related to P and MAT, respectively.  The increasing trends and corresponding magnitudes of runoff were substantially greater in Region 3 than in other regions during this period, while changes in precipitation and temperature did not show obvious in different regions. This indicated that the increase in runoff within Region 3 may have been caused by increased forestlands which experiences higher infiltration rates and increased water conservation and groundwater recharge. Impacts of Climate Change and LUCC on Runoff  Frozen period (November to next April)

 Smelting period (July to October) Impacts of Climate Change and LUCC on Runoff Because there is an extensive area covered by glaciers in the YZRB, the contribution of glacier and snow melt to runoff might play an important role during the melting period.  Runoff and MAT in all regions showed increasing trends during this period, while precipitation exhibited decreasing trends in some regions. This implied that the contribution of glacier and snow melt to runoff might be more important than changes in precipitation.  In fact, glacial area decreased within all regions between 1980 and The decreasing glacial area would positively increase runoff during the melting period, especially for Region 3, which contained the largest glacial area and exhibited the greatest decrease in glacial area.

Regions Frozen periodMelting periodAnnual ΔRΔR P ΔR-ΔR P ΔRΔR P ΔR-ΔR P ΔRΔR P ΔR-ΔR P Region Region Region Region Trends magnitude of runoff depth at different regions in the YZRB (mm/10yr)  Frozen period Region 1: Precipitation affected about 77% of runoff changes Region 2-4: Evapotranspiration which combined effects of increased forest land and air temperature explained more than 80% of runoff changes  Melting period Precipitation is the main factor controlling the runoff process The increasing magnitude of runoff affected by glacier and snow cover was largest within Region 3, and lowest within Region 4. Impacts of Climate Change and LUCC on Runoff  Quantitative analysis

Outline  Introduction  Study area  Materials and Methods  Results  Conclusions

 The effects of climate change and LUCC on runoff were different within different regions during different periods in the Yarlung Zangbo River Basin.  During the frozen period, climate change played an important role in influencing runoff changes within upstream region in the YZRB, accounting for 77%; while evapotranspiration, which combined effects of increased forestland and air temperature explained more than 80% of runoff changes in the middle and lower stream of YZRB.  It may be inferred that forestation could lead to increased runoff in dry seasons. Conclusions

—In future  Data enrichment  Ground observed data —Meteorological data along the elevation gradient —Hydrological variables in the typical catchment  Remote sensing data —More Images with high spatial resolution (5 m, 15m), high temporal resolution —Specific surface products, such as land cover and land use, soil, etc. —Specific inverting products with high precision, such as temperature, precipitation … —More field investigation, such as LUCC, vegetation field investigation for the validation of surface/inverting products…

—In future  Method enrichment  Data processing —Remote sensing interpretation and inversion —Multi-sources data fusion  Eco-hydrological model —Uncertainty analysis —Multi-model combination and improvement of model  For Glacier Melt Tool Model: ----Some Parameters based on the Basin and sub-basin scales ----….

The above results were published as: Liu Z., Yao Z., Huang H. et al, (2014). Land use and climate changes and their impacts on runoff in the Yarlung Zangbo River Basin, China. Land Degradation & Development, 25(3): Thanks You For Your Attention !