One of the world's largest revegetation programs, the Grain for Green Project (GfGP), has been taking place on the Loess Plateau of China since 1999. Such massive revegetation causes changes in the region's hydrological cycle, water availability, and ecological sustainability through enhanced evapotranspiration (ET). Here we quantify effects of the GfGP's revegetation on ET over this water-stressed region. Our approach involves use of a modified Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model, incorporating vegetation dynamics as a new component. The original PT-JPL model has been expanded from site scale to regional scale, thereby allowing its application to the Loess Plateau. The modified PT-JPL model was calibrated and validated against flux tower-measured and water balance-based ET observations. The model performed well at a regional scale with the incorporation of vegetation dynamics. To quantify the net effect of revegetation on evaporative water consumption after the GfGP, we compared scenarios with and without revegetation. We find the revegetation has led to a significant increase in ET across the Loess Plateau, of 4.39 mm/yr averaged over the past 15 years (mean annual precipitation was 464 mm). Compared with the no revegetation scenario, the GfGP revegetation appreciably enhanced evaporative water consumption across the Loess Plateau, by approximately 31 × 10 8 m 3 /yr (or 4.90 mm/yr). Our findings suggest that to maintain ecologically sustainable restoration and rational use of water resources, factors including the strength of revegetation and the relationship between evaporative water consumption and revegetation type should be considered. Key Points:• The PT-JPL model has been upgraded to allow incorporation of vegetation dynamics at a regional scale • The extended PT-JPL model performs well at regional scale • Compared with a no-revegetation scenario, revegetation increases evaporative water consumption byapproximately 31 × 108 m3/yr (4.90 mm/yr) across theLoess Plateau, China Supporting Information:• Supporting Information S1

Estimating long-term average annual water balance at the catchment scale has been an important scientific problem in hydrology and a reliable method for long-term estimates of evapotranspiration (D. Wang, 2012). Water and vegetation in the catchments have reached equilibrium through long-term evolution, so that there is an inextricable relationship between water balance and vegetation change (Gerten et al., 2004). Changes in vegetation affect the elements of water balance, thus vegetation coverage plays an influential role in regulating regional water balance (Heimann & Reichstein, 2008; Seddon et al., 2016). Precipitation (P), evapotranspiration (ET), streamflow (Q), and water storage changes (ΔS) are important components of water balance estimates. Previous studies (e.g., Shao et al., 2019) have demonstrated that vegetation restoration could lead to increases in regional ET over the Loess Plateau, thus changing the water availability. This could potentially exacerbate tensions between water supply and demand in water-stressed regions. Thus, it can be further hypothesized that the vegetation changes may influence the catchment-scale water balance. In addition, the relationship between ΔS and vegetation may be scale dependent and remains unclear, thus studying the time scale of ΔS in vegetation recovery areas is particularly important. The Loess Plateau, a typical arid and semi-arid region, accounts for 6.6% of China's total land area and supports 8.5% of the population (Fu et al., 2011). It is one of the most water scarce regions with the most fragile ecosystems in the world (Y. Wang et al., 2011; B. Zhang et al., 2016). In the past, the Loess Plateau, with its sparse vegetation coverage, frequent summer rains and intensive agricultural practices, suffered unprecedented water scarcity, soil erosion and fragile ecosystems (C. Wang et al., 2016; Z. Yang et al., 2016). These ecological and environmental problems significantly affect ecological environment and socioeconomic

From 1998 to the present, the Chinese government has implemented numerous large-scale ecological programs to restore ecosystems and improve environmental protection in the agro-pastoral ecotone of Northern China (APENC). However, it remains unclear how vegetation restoration modulates intraregional moisture cycles and changes regional water balance. To fill this gap, we first investigated the variation in precipitation (P) from the China Meteorological Forcing Dataset and evapotranspiration (ET) estimated using the Priestly-Taylor Jet Propulsion Laboratory model under two scenarios: dynamic vegetation (DV) and no dynamic vegetation (no-DV). We then used the dynamic recycling model to analyze the changes in precipitation recycling ratio (PRR). Finally, we examined how vegetation restoration modulates intraregional moisture recycling to change the regional water cycle in APENC. Results indicate P increased at an average rate of 4.42 mm yr-2 from 1995 to 2015. ET with DV exhibited a significant increase at a rate of 1.57, 3.58, 1.53, and 1.84 mm yr-2 in the four subregions, respectively, compared with no-DV, and the annual mean PRR values were 10.15%, 9.30%, 11.01%, and 12.76% in the four subregions, and significant increasing trends were found in the APENC during 1995-2015. Further analysis of regional moisture recycling shows that vegetation restoration does not increase local P directly, but has an indirect effect by enhancing moisture recycling process to produce more P by increasing PRR. Our findings show that large-scale ecological restoration programs have a positive effect on local moisture cycle and precipitation.