Revegetation in China s Loess Plateau is approaching sustainable water resource limits

DOI: 1.138/NCLIMATE392 Revegetation in China s Loess Plateau is approaching sustainable water resource limits Xiaoming Feng 1,2, Bojie Fu 1,2*, Shilong Piao 3,4, Shuai Wang 1,2, Philippe Ciais 5, Zhenzhong Zeng 3, Yihe Lü 1,2,Yuan Zeng 6, Yue Li 3, Xiaohui Jiang 7, Bingfang Wu 6 1 State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 185, China 2 Joint Center for Global Change Studies, Beijing 1875, China 3 College of Urban and Environmental Sciences, Peking University, Beijing 1871, China 4 Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 185, China 5 Laboratoire des Sciences du Climat et de l Environnement, CEA CNRS UVSQ, 91191 Gif-sur-Yvette, France 6 Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing 194, China 7 Yellow River Institute of Hydraulic Research, YRCC, Zhengzhou 453, China NATURE CLIMATE CHANGE www.nature.com/natureclimatechange 1

DOI: 1.138/NCLIMATE392 Grain To Green programme investment. The Grain To Green programme (GTGP) is a Chinese national ecological restoration project. By 21 the Chinese government had invested the cumulative total of RMB 192 billion (US$ 31. billion) in GTGP and the planned investment of the next cycle ending in 25 will reach RMB 21 billion ($US 33.9 billion) 1,2. Based on the published reports of the government s investment in infrastructure during 28-211 in Shaanxi Province (RMB 7 billion), Shanxi Province (RMB 1.9 billion), Ningxia Province (RMB 1.3 billion) and that in Gansu Province (RMB 2.9 billion), which cover the main revegetated areas over the Loess Plateau, we estimate that investment in the Loess Plateau region is around 28% of the national total investment in capital projects. By applying this rate, we can estimate that investment in the Loess Plateau region was RMB 53.8 billion (US$ 8.7 billion) by 21 and the next cycle will be RMB 58.8 billion (US$ 9.5 billion). Anthropogenic water demand and water resources. Although vegetation in the Loess Plateau is mostly rain-fed, there is irrigation in the cropland lying in the plain area of the Loess Plateau (e.g., Yinchuan Plain in Ningxia Province, Hetao Plain in Neimenggu Province, Hanzhong Plain in the middle of Shaanxi Province). Irrigation water in both Yinchuan Plain and Hetao Plain is taken from the Yellow River 3,4. Groundwater irrigation mainly occurs in Guanzhong Plain. It is reported that 66.2 percent of cropland in Guanzhong Plain is irrigated, of which 59 percent is from groundwater. The groundwater-irrigated area in Guanzhong Plain is reported to be about 52 km 2 5,6, or.8 percent of the Loess Plateau area. According to the bulletin published by Chinese Ministry of Water Resources (http://www.yellowriver.gov.cn/), water demand for the socio-economic systems of the Loess Plateau region increased from 88.6 1 8 m 3 to 126.4 1 8 m 3 in the period 2-21 with a mean rate of 4% yr -1. The highest increment was in water for domestic use (11% yr -1 ), followed by water for farming, fishing and animal husbandry (2.6% yr -1 ) and industrial use of water (2.2% yr -1 ) (Supplementary Fig.S1). Surface water met 7% of these water demands, with the other 3% coming from groundwater. The Loess Plateau region was self-sufficient in surface water because annual runoff of the Yellow River at Lanzhou Station (171.±47.8 1 8 m 3 ), representing inflow of water, was lower than the outflow at Huanyuankou (216.2±53.6 1 8 m 3 ) (see Supplementary Fig.S2 for the station locations). However, current groundwater withdrawal is unsustainable in the Loess Plateau for two reasons. First, withdrawals for human consumption have already caused a cone of groundwater depletion in the Loess Plateau (Chinese Ministry of Water Resources, http://www.yellowriver.gov.cn/other/hhgb/). Second, replenishment of groundwater is difficult since soil depth in Loess Plateau is 1~2 m on average below the surface with the maximum exceeding 3 m 7. Qian and Zhang 8 predicted that water demand in the Loess Plateau region would continue to increase until year 25, following the increased population, urbanization and the transformation to an industrial society. Qian and Zhang 8 also predicted that per capita water use may decrease with the introduction of water-saving techniques and improvements in the efficiency of industrial infrastructure. Compared to that in 21, water demand for the socio-economic system is expected to have increased by 46.2% in 25, with the highest increment being that of domestic water use (78.6%), followed by industrial use of water (4.7%) and water for farming, fishing and animal husbandry (16.7%). These estimates are supported by other cases in the Loess Plateau region 9,1. 2 NATURE CLIMATE CHANGE www.nature.com/natureclimatechange

DOI: 1.138/NCLIMATE392 SUPPLEMENTARY INFORMATION Water consumption of the socio-economic system on LP (1 8 m 3 ) 18 16 14 12 1 8 6 4 Total water demand Industrial use of water Domestic use of water Water for farming,fishing and husbandry 2 2 21 22 23 24 25 26 27 28 29 21 Year Figure S1. Anthropogenic water demand in the Loess Plateau region. a Runoff (km 3 per yr.) b 9 8 7 6 5 4 3 2 1 Lanzhou station Huayuankou station 195 1953 1956 1959 1962 1965 1968 1971 1974 1977 198 1983 1986 1989 1992 1995 1998 21 24 27 21 Year Figure S2.(a) Location of Lanzhou and Huayuankou stations and (b) their annual runoffs during 195-21. Annual precipitation (mm) 6 5 4 3 2 1 R² =.9 P=.37 R² =.1 P=.9 9 8.8 8.6 8.4 8.2 8 7.8 7.6 7.4 Annual air temperature ( o C) 2 21 22 23 24 25 26 27 28 29 21 Year 7.2 Figure S3. (a) Spatial pattern of annual precipitation trend during 2 21. White indicates areas of no significant change (P>.5). (b) Annual precipitation (blue line) and its non-significant trend (blue dashed lines), annual air temperature (orange line) and its non-significant trend (orange dashed line) for the Loess Plateau during 2-21, indicating stable climate conditions, especially the unchanged precipitation input during this period. NATURE CLIMATE CHANGE www.nature.com/natureclimatechange 3

DOI: 1.138/NCLIMATE392 3 2.8 2.6 Entire Loess Plateau before plantations :Slope=.6, p=.16 Entire Loess Plateau after plantations: Slope=.3,p=.3 GTGP area before plantations:slope=.7,p=.12 GTGP area after plantations:slope=.4,p=.2 LAI 2.4 2.2 2 198 1985 199 1995 2 25 21 Figure S4. Changes in LAI before and after the start of the GTGP plantation programme Table S1 Factors impacting runoff change between 2s and 198~1999. 2s vs 198~1999 ΔTerra(%) ΔDam (%) ΔTree (%) ΔPasture (%) ΔStru (%) ΔPPT(mm) ΔLAI* RS_REV (.36) ΔLAI RS_REV(%) Year ΔTerra and ΔDam are changes in percentage area of terracing and check-dams respectively. ΔTree and ΔPasture are changes in percentage area of new plantation and natural pasture respectively. ΔStru is the combination of ΔTerra and ΔDam indicating the total effect of the structural engineering approach to soil conservation. ΔPPT and ΔPET are changes of annual precipitation and annual potential evaporation over the two compared periods. ΔLAI is change of GLASS LAI for each catchment. RS_REV is the newly planted area observed by Landsat ETM. ΔLAI* RS_REV is product of ΔLAI and RS_REV. ΔLAI, RS_REV and ΔLAI* RS_REV indicate remote sensing detectable ecosystem change. and indicate the variable in the model is significant at P<.1 and P<.5 respectively. Otherwise the variable doesn t meet the.5 significance level for entry into the model of ΔRunoff The Partial R-Square of each variable is given in brackets. indicates variable not included in modelling ΔRunoff. The analysis was conducted with Program SAS 9.2. 4 NATURE CLIMATE CHANGE www.nature.com/natureclimatechange

DOI: 1.138/NCLIMATE392 SUPPLEMENTARY INFORMATION Figure S5. Same as main text Fig. 3, but under RCP2.6 climate scenario. Figure S6. Same as main text Fig. 3, but under RCP6. climate scenario. NATURE CLIMATE CHANGE www.nature.com/natureclimatechange 5

DOI: 1.138/NCLIMATE392 Figure S7. Same as main text Fig. 3, but under RCP8. climate scenario. Figure S8. Spatial distribution of the unconverted croplands before and after the GTGP in the Loess Plateau region. Unconverted croplands were extracted by comparing Landsat TM/ETM-derived land-cover maps in years 2 and 28. The influence of potential evapotranspiration (PET) on runoff in the Loess Plateau region. Using data interpolated from the meteorological observations, we found the temperature increased significantly (p<.1) with a rate of.6 C yr -1 from the 198s to the 2s over the Loess Plateau (Fig. S11a). However, when we estimated the potential evapotranspiration (PET) using the Penman equation, we found no significant PET increase from the 198s to the 2s (slope=1., p>.29). This insignificant PET trend in the Loess Plateau is due to the contribution from other key factors, including net radiation, wind speed and relative humidity. Previous reports for the Loess Plateau 11 and elsewhere, including Australia 12, clearly indicate why fully-physically based PET formulations are needed. Using 6 NATURE CLIMATE CHANGE www.nature.com/natureclimatechange

DOI: 1.138/NCLIMATE392 SUPPLEMENTARY INFORMATION hydrometeorological records of 14 catchments covering the climatically inhomogeneous revegetated area, no significant relationships between PET increase and ET increase (p>.9), or between PET increase and runoff decrease (p>.2) were found (Fig. S11c). This finding should be expected because the Loess Plateau falls within the water-limited area on the Budyko curve, with the dryness index PET/PPT reaching 3.±.5 for the entire Loess Plateau. Moreover, the dryness index has remained stable from the 198s to the 2s (trend of PET/PPT is.5 with the significance level.66, Fig. S11a). Thus evaporation in the Loess Plateau is water-limited rather than being limited by energy input. Annual precipitation (PPT) (mm yr -1 ) (a) 14 12 1 8 6 4 2-2 -4-6 -8-1 -12-14 Annual potential evaporation (PET) (mm yr -1 ) 14 12 1 8 6 4 2 198 1981 1982 14 12 1 8 Potential evapotranspiration 1983 (mm) 198 1984 1981 1985 1982 1986 198 1983 1987 1981 1984 1988 1982 1985 1989 1983 1986 199 1984 1987 1991 1985 1988 1992 1986 1989 1993 1987 199 1994 1988 1991 1995 1989 1992 1996 199 1993 1997 1991 1994 1998 1992 1995 1999 1993 1996 2 1994 1997 21 1995 1998 22 1996 1999 23 1997 2 24 1998 21 25 1999 22 26 2 23 27 21 24 28 22 25 29 26 23 21 27 24 28 25 Temperature 29 26 ( o c) 21 27 28 29 Annual average air 21 temperature ( o c) 6 4 2-2 -2-4 -4 Year Year Year -4-4 -6PET for -6 the PET Loess for the Plateu PET Loess area:slope=1.1,p=.29 for Plateu the Loess area:slope=1.1,p=.29 Plateu area:slope=1.1,p=.29 PET for the PET revegetated for the PET revegetated catchment for the revegetated catchment area:slope=1.5,p=.4 catchment area:slope=1.5,p=.4 area:slope=1.5,p=.4-8 -8-8PPT for -8 the PPT revegetated for the PPT revegetated catchment for the revegetated catchment area:slope=-.1,p=.94 catchment area:slope=-.1,p=.94 area:slope=-.1,p=.94 PPT for the PPT Loess for the Plateu PPT Loess area:slope=-.26,p=.84 for Plateu the Loess area:slope=-.26,p=.84 Plateu area:slope=-.26,p=.84-1temperature -1Temperature for the Loess Temperature for the Plateau Loess for area:slope=.6,p<.1 Plateau the Loess area:slope=.6,p<.1 Plateau area:slope=.6,p<.1-12 Temperature for the revegetated Temperature catchment for the revegetated area: slope=.6,p<.1-12 Temperature for the revegetated catchment catchment area: slope=.6,p<.1 area: slope=.6,p<.1-12pet/ppt -12PET/PPT for the revegetated for PET/PPT the revegetated catchment for the revegetated catchment area:slope=.4,p=.66 area:slope=.4,p=.66 catchment area:slope=.4,p=.66 PET/PPT PET/PPT for the Loess for PET/PPT the Plateu Loess area:slope=.5,p=.66 for Plateu the Loess area:slope=.5,p=.66 Plateu area:slope=.5,p=.66-14 -14-16 -16 16 12 8 4 16 12 8 4 16 12 8 4-4 -8-12 -16 Ratio of annual potential evaporation and annual precipitation (PET/PPT) (b) (c) ET increase (mm yr -2 ) 6 4 2 13 35 4 12 3 3 9 3 2 12 25 1 8 4 6 2 2 1 14 71 8 5 6 15 11 9 11 1-2 1 142 5 4 6 8 13 5 7-2 PET increase (mm yr -2 ) Runoff decrease (mm yr -2 ) Figure S9. Trend of air temperature, potential evapotranspiration (PET), precipitation (PPT) and the dryness index (PET/PPT) for the Loess Plateau area and the revegetated area from the 198s to the 2s. Annual temperature and precipitation were derived from daily records of average air temperature and precipitation, which were obtained from 172 stations within and near the Loess Plateau and further interpolated onto a map covering the Loess Plateau area at 1-km resolution with ANUSPLIN 3.1. The revegetated area contains 14 catchments with long term hydrometeorological records. PET was calculated based on the Penman equation. (b) Location of the 14 catchments with revegetation and (c) the relationship between the increase in PET and increase in ET, as well as that between increase in PET and decrease in runoff during 2-21. The PET and ET are annual averages of the Loess Plateau. Each number in green in (c) represents dot of (PET increase, ET increase) of the corresponding catchment in (b), and that in blue represents dot of (PET increase, Runoff decrease). NATURE CLIMATE CHANGE www.nature.com/natureclimatechange 7

DOI: 1.138/NCLIMATE392 Trend in groundwater: We used two different approaches to estimate the change in groundwater storage in the Loess Plateau. First, we estimated the anomaly of groundwater storage by subtracting from total water storage anomalies (TWSA) the anomalies of soil moisture, snow water equivalent and runoff 13. TWSA was derived from the latest release (RL5) of the Gravity Recovery and Climate Experiment (GRACE) satellite 14,15. Processing of GRACE data includes truncation at 6 o, destriping to remove north-south bands, filtering to remove high frequency noise and 3 km Gaussian filter to suppress the spatial noise. A land-grid-scaling factor is provided for restoring signal loss of GRACE data during truncation and filtering. Three GRACE data processing centres are the University of Texas Center for Space Research (CSR), NASA Jet Propulsion Lab (JPL) and the German Research Centre for Geosciences (GFZ). The GRACE TELLUS website provides gridded monthly GRACE RL5 at 1 degree plus scaling factor on original CSR, JPL and GFZ data. TWSA in this study are average of the timing of gridded GRACE RL5 and scaling factor over the entire Loess Plateau. Soil moisture between the surface and a depth of 3.2 m, snow water equivalent and runoff were taken from the Community Land Model (CLM) of the Global Land Data Assimilation System (GLDAS) 16. Because no GRACE satellite data were available before March 22 and complete annual observations were started in 24, annual change in the GRACE-groundwater storage was only considered during the period 24-21. Secondly, we analysed water table depth data during the period 2-21. These data were reported by the Ministry of Water Resources from seven in situ measurement stations, both for shallow (stations at Yinchuan, Songtie, Taiyuan and Yuncheng) and deep water tables (stations at Peidong, Xinghua and Luqiao) over the Loess Plateau (Yellow River Water Resources Bulletin, http://www.yellowriver.gov.cn/other/hhgb/). As shown by Fig. S1, neither the GRACE-derived groundwater storage anomaly nor the variation of the water table in the Loess Plateau varied significantly during the period (P >.1). We conclude that revegetation in the Loess Plateau does not disturb the local groundwater, which is further supported by the huge gap between tree rooting depth (~4 m) and soil depth (1~2m on average with the maximum exceeding 3 m) in this area 7. 8 NATURE CLIMATE CHANGE www.nature.com/natureclimatechange

DOI: 1.138/NCLIMATE392 SUPPLEMENTARY INFORMATION GRACE-derived monthly groundwater storage anomaly (mm) 23 18 13 8 3-2 -7 8 6 GRACE-derived annual groundwater storage anomaly (mm) 4 2-2 -4 CSR GFZ JPL 6 1 Variation of ground water table (m) GRACE-derived annual groundwater -4 storage anomaly -9 Variation of shallow ground water -6 table Variation of deep ground water table -8-14 2 22 24 26 28 21 Year -12 22 23 24 25 26 27 28 29 21 211 Month Figure S1. GRACE-derived groundwater storage anomaly in the Loess Plateau. The inset graph at the top shows the non-significant variation of both GRACE-derived groundwater storage and water table depth (P>.1). GRACE-derived annual groundwater storage in the inset is average of those derived from CSR, GFZ and JPL. Variations of water table depth are reported by the Ministry of Water Resources from seven in situ measurement stations over the Loess Plateau. The green line on the inset shows the average variation of stations at Yinchuan, Songtie, Taiyuan and Yuncheng for shallow water tables and the blue line shows the average variation of stations at Peidong, Xinghua and Luqiao for deep water tables. Figure S11 The 32 catchments used in main text. The 23 catchments in Fig. 2d are those with streamflow records covering years both before and after revegetation, spanning longer than half of the length of each period. References for supplementary material 1. Li, Y.C. Grain for Green program is a great concrete action towards the ecological civilization in China: summary of a decade program implementation. Forest. Const. 27, NATURE CLIMATE CHANGE www.nature.com/natureclimatechange 9

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