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Highlights • We analyze the spatiotemporal pattern of the ECC on the Loess Plateau. • The average annual ECC is 577 ± 124 g C m−2 yr−1 during 1982–2012. • Due to revegetation, 26 counties have exceeded the ECC threshold. • 138 counties have water competition between ecosystems and socio-economic systems. • Under future climate change and growing water demand, ECC will increase by 6–36%. Abstract Revegetation, especially afforestation, has served as an important tool for controlling desertification. However, revegetation in water-limited regions will inevitably reduce the water available for socio-economic systems, which is poorly considered in decision-making on sustainable ecosystem management. This paper proposed a framework to determine the threshold of vegetation productivity (i.e., ecosystem carrying capacity), corresponding to available water resources for ecosystems (i.e., annual precipitation minus water demand for socio-economic systems) on the Loess Plateau. The average annual ecosystem carrying capacity (ECC) during 1982–2012 is 577 ± 124 g C m−2 yr−1, with spatial gradients increasing from northwest to southeast. Vegetation in rocky mountain areas has the largest value of 833 ± 200 g C m−2 yr−1. Factorial analysis suggests that changes in precipitation and human water use contributed to 55% and 45% of the multi-decadal changes in regional ECC, respectively. Meanwhile, due to revegetation, 26 counties on the Loess Plateau, mainly in the southeast and eastern parts, have exceeded the ECC threshold during the study period. An additional 138 counties have a high potential for water competition between the ecosystems and socio-economic systems. At the regional scale, there are 9 years (∼30% of the study period) during which the ECC threshold has been exceeded, especially after 1997. Considering the climate change in the future and the growing demand for water in socio-economic systems, the corresponding ECC threshold will increase by 6–36%. We believe that these findings can provide reference for policy-makers to make decisions towards ecosystem sustainability while meeting human needs for water resources. [ABSTRACT FROM AUTHOR]

Abstract Reliable attribution of changes in streamflow is fundamental to our understanding of the hydrological cycle and is needed to enable decision makers to manage water resources in a sustainable way. Here, we used a new attribution method based on the Budyko framework (complementary method) to quantify the contributions of climate change and human activities to the changes in annual streamflow in 22 catchments on China's Loess Plateau during the past three decades. Our results showed that after the Grain-for-Green (GFG) project, the annual streamflow decreased by 36% on average (3–72%), with reductions being more intense in northern catchments. The sensitivity of streamflow to precipitation and potential evapotranspiration also decreased, with a mean rate of −0.7 mm yr−1/mm yr−1 and −0.2 mm yr−1/mm yr−1, respectively. Using the upper and lower bounds of the human effects on streamflow from the complementary method as a reference, we found that these effects at half of the stations were under- or over-estimated by the total differential method. The contribution analysis from the complementary method showed that although human activities decreased streamflow by 26% (or 54% as a relative value) on average, the contribution of potential evapotranspiration alone to the decrease in streamflow was 9% (42%), highlighting the important role of increasing atmospheric moisture demand in the water cycle. In addition, the 5-year incremental analysis showed that the impacts of climate and human activities on streamflow had strong spatiotemporal variability. Graphical abstract Unlabelled Image Highlights • Annual streamflow significantly decreased by 36% on average after the GFG project. • Half of the stations in estimating human effect are underestimated or overestimated by the total differential method. • Potential evapotranspiration alone decreased streamflow by 9% (or 42% as relative value). [ABSTRACT FROM AUTHOR]

Abstract Remote sensing based vegetation index provides a practical method for the monitoring of vegetation dynamics at regional and global scales. Here, using a long-term remotely sensed normalized difference vegetation index (NDVI) dataset, we quantified the vegetation changes in the Loess Plateau (LP) over the last three decades (1982–2015), which includes the period before the Chinese"Grain for Green Program"(GGP) was launched (1982–1999), and the period after the GGP (1999–2015). The correlations between the NDVI and four climate related variables, i.e., precipitation, temperature, root-soil moisture (RSM), and a drought proxy-standardized evapotranspiration deficit index (SEDI), were also examined. The results indicated that, (i) the GGP strongly changed the vegetation in the LP. The growing-season mean NDVI (GSM-NDVI) and the annual mean NDVI (AM-NDVI) decreased slightly before the GGP launched in 1999, with slopes of −3.38 × 10−3 and − 8.00 × 10−4 year−1, respectively. However, they showed slight and significant (p < 0.05) increases after the GGP, with slopes of 4.75 × 10−3 and 2.32 × 10−3 year−1, respectively. (ii) Climate change (i.e., warming and drying) resulted in adverse effects on vegetation in the LP during the period before the GGP. However, the observed changes (i.e., wetting and reduced drought) exerted positive effects on the vegetation during the period after the GGP. (iii) Inter-annual variations of spatially averaged NDVI over the LP were primarily determined by RSM rather than any other climate related variables. In the southeastern LP, the inter-annual variation of GSM-NDVI was mainly determined by precipitation and SEDI, while the inter-annual variation of AM-NDVI was mainly caused by SEDI and RSM. Inter-annual variations of both GSM-NDVI and AM-NDVI were mainly determined by SEDI and RSM in the northwestern LP, and by temperature in the southwestern LP. Graphical abstract Unlabelled Image Highlights • The Grain for Green Program (GGP) greatly changed vegetation in the Loess Plateau. • Climate changes exerted adverse effects on vegetation in the LP before the GGP. • Wetting and reduced drought positively affected vegetation in the LP after the GGP. • The inter-annual variation of NDVI was primarily determined by soil moisture. [ABSTRACT FROM AUTHOR]

As the most frequent and longest-lasting climate-related disasters, droughts are complex processes caused by hydrological imbalance, and have significant effects on ecosystem function and socioeconomic development. However, most conventional satellite-based drought indices and combined drought indices are mechanically constrained by the fact that they were developed and evaluated for a specific climate or critical ecological region, especially in China. A comprehensive drought index should be developed for extensive application in different climate-hydrology regions. To address this problem, an optimised principal component analysis method (PCA-RF) was proposed to support drought assessment across the transitional area between the humid and arid regions in central China, including the Loess Plateau (LP) and Qinling Mountains (QL). This method eliminated the causal relationships of non-linear changes for multi-aspect parameters such as land surface temperature, precipitation and soil moisture, and was used in developing a new index named "Meteorological drought index by PCA-RF methods (PMDI)". The results showed that PMDI had higher correlations and lower root mean square error than other drought indices (established using the empirical-weights method) with the 1-month standardized precipitation evapotranspiration index (SPEI-1). That means PMDI performed well in meteorological drought monitoring. Additionally, the normalized difference vegetation index (NDVI) and solar-induced chlorophyll fluorescence (SIF) were utilised to evaluate PMDI effectiveness in detecting vegetation response to drought, which represents agricultural drought. The results indicated that correlations between PMDI and vegetation indices (VIs) were stronger when severe or extreme droughts occurred, and that their relationships were affected by the high spatiotemporal heterogeneity in vegetation change over the LP and QL. Overall, PMDI was shown here to be a very suitable index for monitoring meteorological drought (short-term) and has effective action in capturing the response of vegetation signals to agriculture drought events (long-term). Given the excellent performance of PMDI in diverse climate-hydrology conditions of our study regions, we concluded that the PMDI has considerable potential as a drought monitoring methodology on a larger spatial scale. • A new drought index was developed (PMDI), which integrated multiple sources of information describing different aspects. • PMDI performed well in different climate-hydrology regions for short- and long-term drought monitoring. • PMDI has reasonably good potential applicability in drought monitoring on a larger spatial scale. [ABSTRACT FROM AUTHOR]

Agricultural water resource, mainly consumed through evapotranspiration, plays a critical role in agricultural production of arid and semiarid regions. Quantifying the changes of evapotranspiration in cropland (ETc), and its driving factors, may provide rich information for improving human land-use and water resource management. Here we first investigated the multi-year (2000–2015) changes in the ETc (mm yr−1) and associated driving factors of the Loess Plateau (LP), using a combination of the Vegetation Interfaces Processes model and a factorial analysis of variance. We found that the ETc of the LP showed a significant upward trend of 0.31 km3 yr−2 (3.33 mm yr−2) (p <.05) over the last 16 years, mainly driven by cropland changes (3.77% per year), which combined the contribution of cropland area changes and cropland leaf area index (LAIc) changes. We then examined the changes of the dominant driving factor: cropland, and results indicated that the cropland changes consisted of the decrease in cropland area (net decrease of 10.50 × 103 km2) and the increase in LAIc (increased by 10.72%), which suggest the actual contribution of the ETc uptrend was the increasing LAIc. Our further analysis on the causes of the increasing LAIc by correlating the LAIc with land-use management factors revealed that the cropland greening on the LP showed high positive correlations with the increasing inputs of total power of agriculture machinery and farm plastic film, followed by chemical fertilizer. The increase of LAIc was also promoted by the increased ratio of the garden fruits output to total crops output (increased by 67.12%) and multiple cropping (increased by 21.66%). These results suggest that the ETc uptrend can be related to the agricultural intensification. Our study highlights the need for a realistic representation of socio-economic development and human land-use practices in the sustainable optimal allocation of agricultural water resources on the LP. Unlabelled Image • ET in cropland (ETc) showed upward trend over the Loess Plateau from 2000 to 2015. • Land-use optimization drives cropland greening and promotes multi-year rise of ETc. • Socioeconomic development and land-use practice affect agricultural water allocation. [ABSTRACT FROM AUTHOR]