• Energy Research
• environmental engineering close
• Chinese Academy of Sciences close

AbstractThe ongoing changes in vegetation spring phenology in temperate/cold regions are widely attributed to temperature. However, in arid/semiarid ecosystems, the correlation between spring temperature and phenology is much less clear. We test the hypothesis that precipitation plays an important role in the temperature dependency of phenology in arid/semiarid regions. We therefore investigated the influence of preseason precipitation on satellite‐derived estimates of starting date of vegetation growing season (SOS) across the Tibetan Plateau (TP). We observed two clear patterns linking precipitation to SOS. First, SOS is more sensitive to interannual variations in preseason precipitation in more arid than in wetter areas. Spatially, an increase in long‐term averaged preseason precipitation of 10 mm corresponds to a decrease in the precipitation sensitivity of SOS by about 0.01 day mm−1. Second, SOS is more sensitive to variations in preseason temperature in wetter than in dryer areas of the plateau. A spatial increase in precipitation of 10 mm corresponds to an increase in temperature sensitivity of SOS of 0.25 day °C−1 (0.25 day SOS advance per 1 °C temperature increase). Those two patterns indicate both direct and indirect impacts of precipitation on SOS on TP. This study suggests a balance between maximizing benefit from the limiting climatic resource and minimizing the risk imposed by other factors. In wetter areas, the lower risk of drought allows greater temperature sensitivity of SOS to maximize the thermal benefit, which is further supported by the weaker interannual partial correlation between growing degree days and preseason precipitation. In more arid areas, maximizing the benefit of water requires greater sensitivity of SOS to precipitation, with reduced sensitivity to temperature. This study highlights the impacts of precipitation on SOS in a large cold and arid/semiarid region and suggests that influences of water should be included in SOS module of terrestrial ecosystem models for drylands.

Plant phenological events are sensitive indicators of climate change, and their change could markedly affect the structure and function of ecosystems. Previous studies have revealed the spatiotemporal variations in the phenological events of woody plants. However, limited studies have focused on the phenophases of herbaceous plants. In this study, by using a meta-analysis method, we extracted information about the phenological changes in herbaceous plants in China's grasslands from existing studies (including the period, station, species, phenophases, phenological trends, and climatic determinants) and analyzed the patterns manifested in the dataset. The results showed that the spring phenophases (e.g., first leaf date and first flowering date) of the herbaceous plants mainly advanced over the past 30 years, but a large difference existed across grassland types. The spring phenophases of forages (species from the Cyperaceae, Gramineae, and Leguminosae families) became earlier in the desert steppe and alpine steppe but showed no apparent trends in the alpine meadow and even became later in the meadow steppe and typical steppe. In most cases, the increase in spring temperatures and precipitation promoted the greening up of herbaceous plants, while sunshine duration was positively correlated with the green-up date of herbaceous plants. For the autumn phenophases, the proportions of the earlier and later trends were very close, but the trends varied among the grassland types. The leaf coloring dates of the forages were delayed in the meadow steppe and alpine steppe but showed no distinct pattern in the typical steppe or alpine meadow and even became earlier in the desert steppe. In most cases, the increase in growing season temperature led to an earlier leaf coloring date of the herbaceous plants, but the increase in the preseason precipitation delayed the leaf coloring date. Our results suggested that the phenophases of herbaceous plants have complicated responses to multiple environmental factors, which makes predicting future phenological changes difficult.

Vegetation is a crucial component of terrestrial ecosystems, and its changes are driven mainly by a combination of climate change and human activities. This paper aims to reveal the relationship between vegetation and climate change by using the normalized difference vegetation index (NDVI) and standardized precipitation evapotranspiration index (SPEI), and to find the cause of vegetation change by performing residual analysis on the Loess Plateau during the period from 2000 to 2016. The results showed that the NDVI on the Loess Plateau exhibited an increase of 0.086 per decade, and an increasing trend was observed across 94.86% of the total area. The relationship between the NDVI and SPEI was mainly positive, and the correlation increased as the time scale of the SPEI lengthened, indicating that long-term water availability was the major climate factor affecting vegetation growth. Residual analysis indicated that climate change was responsible for 45.78% of NDVI variation, while human activities were responsible for 54.22%. In areas with degraded vegetation, the relative roles of climate change and human activities were 28.11% and 72.89%, respectively. In addition, the relative role of climate change increased with an increase in the time scales, implying that the long-term NDVI trend was more sensitive to climate change then the short-term trend. The results of this study are expected to enhance our understanding of vegetation changes under climate change and human activities and provide a scientific basis for future ecological restoration in arid regions.

Study Region:: Hulun Lake, the fifth largest lake in China. Study Focus:: The notable decline in water level (WL) caused by climate change is the primary challenge faced by Hulun Lake. However, the contribution of climate to water loss and its driving mechanisms remain unclear. The impact of climate on WL change was investigated using wavelet analysis and structural equation models. New Hydrological Insights for the Region:: In the past 60 years, the increasing potential evapotranspiration (ETp) caused by warming climate was the main reason for the WL decline (r=−0.67). For period I (1961–1997), reduced runoff due to increasing ETp caused an overall decrease in WL (r = 0.41). During the mid-1980s, the increase in rainfall driven by ENSO (r = −0.66) caused a slight increase in WL (r = 0.31). For period II (1998–2020), deforestation, farmland and urban area expansion were the main drivers behind the significant increase of ETp in the watershed (r = −0.22), which leads to reduced runoff and, consequently, a significant decrease in WL. The influence of climate on WL change weakened compared with that in the first period due to land use change (r = −1.08).

Inter‐basin water transfer projects (IBWTPs) offer one of the most important means to solve the mismatch between supply and demand of regional water resources. IBWTPs have impacts on the complex ecosystems of the areas from which water is diverted and to which water is received. These impacts increase damage or risk to regional ecological security and human wellbeing. However, current methods make it difficult to achieve comprehensive analysis of the impacts of whole ecosystems, because of the long distance between ecosystems and the inconsistency of impact events. In this study, a model was proposed for the analysis of the impacts of IBWTPs on regional ecological security. It is based on the telecoupling framework, and the Driver‐Pressure‐State‐ Impact‐Response (DPSIR) model was used to improve the analysis procedure within the telecoupling framework. The Middle Line of the South‐to‐North Water Diversion Project was selected as a case study to illustrate the specific analysis procedure. We realized that information sharing is a key issue in the management of regional security, and that the ecological water requirement, in the form of a single index, could be used to quantitatively assess the impacts on ecological security from IBWTPs.

Lakes on the Tibetan Plateau (TP) are an indicator of global climate change. The study on the factors driving lake change on the TP can help us understand its response to climate change. In this study, Landsat and ICESat data were used to obtain the variations of area, water level, and storage of Hala Lake and the area of glaciers in the Hala Lake Basin during 1987–2018. Combined with meteorological data, climate change trends and the factors driving Hala Lake change in the last 30 years were analyzed. The contribution of glacier mass loss to lake recharge was estimated by the water balance of Hala Lake. The results showed that Hala Lake has experienced three stages: slight expansion (1987–1994), shrinkage (1995–2001) and rapid expansion (2002–2018) during the study period. The rate of glacial melting continued to decline during the study period. Precipitation was the main factor that drove the hydrological characteristic changes in Hala Lake. The step change points of annual precipitation and temperature occurred in 2001, almost the same time that Hala Lake began expanding rapidly.

Dune-interdune is the main landscape pattern of desert areas, such as the Horqin sandy land of Northeastern China. Exploring the temporal and spatial variation of the water balance is crucial for efficient vegetation restoration at the micro-landform scale. The SWMS-2D model was used to estimate the seasonal variations of the water balance including evapotranspiration, soil water storage changes, lateral flow and drainage, and to examine the effects of micro-landforms (i.e., the top, upper, down, and bottom positions of the dune slope, and the interdune lowland area) on these components from May to October 2013 and 2015. Results showed that the soil water content was sensitive to rainfall pulses, particularly large precipitation events. Over 70% of the total evapotranspiration occurred from June to August, with a maximum daily value of 6.56 mm. At a monthly scale, evapotranspiration was not synchronous with precipitation. The ratio of evapotranspiration to precipitation was 1.84, 0.39, 2.49, 0.93, 2.26, and 1.14 in May, June, July, August, September, and October 2013 (a wet year), respectively; and 2.40, 1.11, 0.69, 2.14, 1.07, and 1.11 in 2015 (a dry year), respectively. The components of the water balance were significantly different among different micro-landforms. Evapotranspiration of a lowland area was greater than that in other micro-landforms, and the value in the wet year (2013) was significantly greater than that in the dry year (2015). However, water consumption in the lowland area was similar in both years. At the top, upper, down, and bottom positions of the dune slope, the ratio of evapotranspiration to precipitation in the wet year (2013) was 96%, 97%, 86%, and 96%, respectively; while in the dry year (2015), the ratio was 103%, 103%, 88%, and 104%. Therefore, in the dry year, evapotranspiration was generally larger than precipitation, indicating that almost all water from precipitation was evaporated. The lateral flow of the root zone from top to bottom accounted for only a small portion of water budget at the growing season scale. The results could be generalized to other similar region with corresponding model calibration, and would help to reveal seasonal variations of water balance components under the local topography, climate, soil, and vegetation conditions.

In an attempt to alleviate water scarcity, the government of China has introduced a water plan for the year 2030. Based on a dynamic computable general equilibrium model, this paper investigates how conservation of irrigation water, grain production, and the welfare of rural households will be affected by planned reductions to the irrigation water subsidy between 2018 and 2030. Four policy instruments, namely quantitative control (QC), quantitative control with a subsidy reduction (QC-SR), price control (PC), and price control with a subsidy reduction (PC-SR) are employed in the model. Most existing research has found that reducing the irrigation subsidy will lead to significant negative impacts to the agricultural economy, and especially to rural households. These predicted negative impacts are a barrier to agricultural water policy pricing reform. However, the results of this research show that a provincial subsidy reduction to 1% between 2018 and 2030 will have an insignificant impact on agricultural production as well as rural household incomes and welfare, despite the subsidy rate currently accounting for more than 90% of the total irrigation value at the macro level in most provinces. Furthermore, PC will create a demand for irrigation water, which is predicted to rise to more than five times the agricultural water planning level currently set for 2030, and PC-SR will not achieve the agricultural water planning goal.