Analysis on Relationship between Lake Change and Climate Change in the Ulan Buh Desert

Environmental changes in the Ulan Buh Desert, southern Inner Mongolia, China since the middle Pleistocene based on sedimentology, chronology and proxy indexes

Contents of Volume 36 and Index

A clear understanding of the spatiotemporal evolution and driving factors of ecosystem service value (ESV) and the landscape ecological risk index (ERI) can effectively link human well-being and ecosystem security, which is essential for sustainable ecosystem management. Based on multitemporal land use data (1990, 2000, 2010, and 2018), the spatiotemporal evolution of ESV and the ERI in the Ulan Buh Desert was evaluated. The driving forces of ESV and the ERI were quantitatively evaluated by the Geodetector model. The results show that 1) from 1990 to 2018, total ESV in the Ulan Buh Desert increased from 7.00×108 yuan to 11.09×108 yuan. Low-ESV areas accounted for approximately 72.28% of the study area. High-ESV and moderate-high-ESV areas were mainly distributed along the Yellow River and the northeastern region. 2) During the study period, the ecological risk of the Ulan Buh Desert generally decreased; only the ecological risk of the northeastern region improved significantly, and high-risk areas were mainly distributed across sand dunes located in the middle of the desert. 3) There was a negative correlation between ESV and the ERI in the study area, and the main relationship was low value-high risk. 4) Driving force analysis results show that natural and human impact factors jointly affected the spatiotemporal differentiation of ESV and the ERI in the Ulan Buh Desert. Among the influencing factors, the interaction between the distance to a highway and annual precipitation had the strongest impact. The implementation of relevant policies in the study area should be guided by ESV and the ERI, and the protection and restoration of various ecosystems in the study area must be strengthened.

The Ulan Buh Desert, as one of China's eight significant deserts, is situated in the country's northwestern region and encompasses a diverse array of landscapes, including various desert types, vegetation, water bodies, and other landforms. This diversity is crucial for the ecological integrity and safety of the Yellow River Basin. The desert is notably constrained by water availability, and there has been a notable expansion in the degree of human activities, particularly regarding agricultural development, in the area.Over the past 32 years, studies tracking the temporal and spatial variations of the Normalized Difference Vegetation Index (NDVI) in the Ulan Buh Desert have revealed a consistent increase in vegetative cover. Through the analysis of drivers such as climate change and human activity, it has been determined that temperature exhibits a positive correlation with NDVI, a relationship that has strengthened progressively over the years. Conversely, precipitation's influence on NDVI has been relatively insignificant. On the human activity front, contributions to NDVI changes have grown considerably, with such activities accounting for nearly a 50% increase in the vegetative index, suggesting that human interventions are increasingly aligning with ecological rehabilitation and positive environmental outcomes.By scrutinizing the ecological consequences of both natural processes and human endeavors on the Ulan Buh Desert, insights gleaned can offer actionable recommendations for ecological restoration efforts, ensuring the sustainable management and recovery of this vital region.

Desert farmland provides food for desert areas, but water is the main limiting factor of this region, thus desert farmland has an extremely fragile ecological environment. This study investigated the temporal and spatial variations of vegetation NDVI (Normalized Difference Vegetation Index) in the Ulan Buh Desert, China, from 1990 to 2022, using long-term Landsat satellite data obtained from the Google Earth Engine platform and local statistical data. The results showed that from 1990 to 2022, the NDVI exhibited relatively small fluctuations and a steady increase. Furthermore, the study analyzed the impact of climate factors, namely precipitation and temperature, on NDVI, and collected the groundwater lever changes under irrigation and farmland development. The results demonstrated a positive correlation between NDVI and both precipitation and temperature from 1990 to 2006. The study area experienced an overall trend of increasing humidity. Specifically, from 1990 to 2006, significant positive correlations with precipitation and temperature were observed in 4.4% and 5.5% of the region, respectively. From 2007 to 2022, significant positive correlations were observed in 5.4% and 72.8% of the region for precipitation and temperature, respectively. These findings suggest that temperature has become increasingly influential on vegetation NDVI, while the impact of precipitation remains relatively stable. Moreover, the study assessed the impact of human activities on vegetation NDVI. The results revealed that from 1990 to 2006, human activities contributed to 43.1% of the promotion of local vegetation NDVI, which increased to 90.9% from 2007 to 2022. This study provides valuable insights into the dynamics of vegetation in the Ulan Buh Desert and its response to climatic changes and human activities. The findings highlight the significance of climate conditions and human interventions in shaping the vegetation dynamics in the region, offering essential information for ecological restoration and conservation efforts.

To combat desertification, an understanding of its current development is necessary, including that of causative factors associated with climate change and increasing human activity. Whereas, there is an ongoing debate surrounding impact factors for change in vegetation and desertification in arid regions. The present study assesses the spatiotemporal characteristics of vegetation change in the Ulan Buh Desert, northwest China. Driving factors for desertification were discussed using the Global Inventory Monitoring and Modeling System Normalized Difference Vegetation Index (GIMMS NDVI) and SPOT Vegetation NDVI datasets, high-resolution satellite images, and meteorological and socioeconomic data in the period 1982–2018. The results show a trend of overall greening, with increasing trends at rates between 0.0008/year and 0.0013/year indicated by the two NDVI datasets and with a corresponding reduction in dune activity. The spatial variations of two NDVI datasets verified the significantly greening trend in the northern and southern areas of the desert. Human activity was observed to have impacted vegetation dynamics. It is predicted that the implementation of ecological projects will contribute to the restoration of vegetation during a warmer, wetter climate trend. However, the reduction of wind strength played a dominant role in vegetation greenness and dune stability in the Ulan Buh Desert. The present study revealed the spatiotemporal characteristics of vegetation variations and the driving factors for desertification in arid regions.

Early–middle Holocene lake-desert evolution in northern Ulan Buh Desert, China

Quartz and K-feldspar optical dating chronology of eolian sand and lacustrine sequence from the southern Ulan Buh Desert, NW China: Implications for reconstructing late Pleistocene environmental evolution

<p>The windbreak system is a major component of successful agricultural systems in arid deserts throughout the world. Ulan Buh Desert is one of the eight biggest deserts in China, and the oases there offer residence and cropland for over 90% of the local residents. However, due to climate change and human disturbances, the Ulan Buh Desert continues spreading to the south, bringing more pressure on the windbreak systems there. Meanwhile, the Chinese government put much effort into greening the desert, establishing artificial shrubs to prevent dune movement and soil loss. How microclimate in the cropland-windbreak-desert system responded to human activities and climate change has rarely been studied. In this study, we investigated the microclimate change dynamics across the cropland-windbreak-desert transition zone during the past 38 years. Two 50 m climatological towers, located in the same distance inner and outside a shelterbelt, have continuously monitored climatic factors, including air temperature, soil temperature, relative humidity, precipitation, evaporation, layered wind speeds, etc., and aeolian erosion related factors, such as layered dustfall. The long-time fluctuations of the inside and outside climatic factors have been analyzed, and the global climate change data, local land-use history, as well as the record of afforestation activities implemented by government and local people, were also collected. The results revealed that both the inside and outside windbreak air temperatures and soil temperatures increased during the past 38 years, which agrees with the global warming phenomenon. The inner windbreak air temperature is consistently lower than the outer windbreak areas, and the temperature difference is biggest in summer and smallest in winter. However, the soil temperature difference between the outside and inner windbreak is unstable. In 1995, 2002, and 2004, the dune areas even had lower soil temperature than the inner cropland. The precipitation is 0.5~100.7mm higher in cropland and the evaporation is lower in cropland when comparing to outside dune areas, but their annual variations changed greatly. The wind speed and erosion rate are significantly lower in cropland than desert dune areas, and the seasonal change exhibited a bimodal curve pattern. The results suggest that the cropland-windbreak-desert transition zone responded to global climate change simultaneously. Although the shelterbelt still creates a favorable regional climatic condition for the cropland, the differences between the inner and outer windbreak areas narrowed during the past 10 years. The aeolian erosion rate reduced significantly in outside windbreak dune areas, which may largely attribute to the artificial Haloxylon ammodendron communities planted at the southeastern margin of the desert.</p>

Eggs of Aedes triseriatus mosquitoes are stimulated to hatch when inundated with water, but only a small fraction of eggs from the same batch will hatch for any given stimulus. Similar hatching or germination patterns are observed in desert plants, copepods, rotifers, insects, and many other species. Bet hedging theory suggests that parents stagger offspring emergence into vulnerable life history stages in order to avoid catastrophic reproductive failures. For Ae. triseriatus, a treehole breeding mosquito, immediate hatching of an entire clutch leaves all of the parent's progeny vulnerable to extinction in the event of a severe drought. Natural selection has likely favored parents that pursued a bet hedging strategy where the risk of reproductive failure is distributed over time. Considering treehole mosquitoes, bet hedging theory could be used to predict that hatch delay would be positively correlated with the likelihood of drought. To test this prediction, we collected Ae. triseriatus from habitats that varied widely in mean annual precipitation and exposed them to several hatch stimuli in the laboratory. Here we report that, as predicted, Ae. triseriatus eggs from high precipitation regions showed less hatch delay than areas of low precipitation. This strategy probably allows Ae. triseriatus to cope with the wide variety of climatic conditions that it faces in its extensive geographical range.

Lake Ulaan is a terminal lake at the eastern end of the Valley of Lakes in the northernmost Govi region, and the lake plays a valuable role in surface water resource of southern Mongolia. Lake Ulaan basin has been strengthened with the warming and drying since the mid-1970s. Lake Ulaan experienced changes of its area and sedimentation dynamics during the Holocene. The lake lost an area of 18.2 km2 during the last four to five decades, and it disappeared between the mid-1980s and the mid-2010s. In short, Lake Ulaan has been a playa lake during the last half century. The playa lake condition coincides with regional climate change and local warming since 1975 and drying since 1974. The linear regression analysis shows that the lake area between 1986 and 2014 had no clear relationships with the annual average air temperature (R2 = 0.0833) and precipitation (R2 = 0.0063). The correlation analysis shows that the lake area during 1986–2014 had a weak positive correlation with air temperature (r = 0.288) but no clear correlation with precipitation (r = 0.07). The geochemical analysis shows the dominance of alkali and alkaline earth metals in Lake Ulaan sediments and the higher degree of chemical weathering in the lake margin than the lake center. The chemical maturity of the Lake Ulaan sediments shows the shift from semiarid to arid climate conditions in the lake basin. Lake Ulaan contributes to the understanding of the response of the local hydrological system to climate change, and it helps in revealing the landscape evolution of the Valley of Lakes in southern Mongolia over geological time scales.KeywordsLake UlaanOngi RiverValley of LakesGovi regionClimate changeSouthern Mongolia

This comprehensive study delves into the intricate relationship between climatic factors and the dynamic changes in lakes across the Kerch Peninsula. By analyzing annual mean temperature, annual mean precipitation, and their impact on lake area, this research uncovers significant insights. Key findings include a strong inverse correlation between rising annual mean temperature and reductions in the lake area. With every 1-degree Celsius increase in temperature, the average lake area decreases by 0.302 square kilometers. The analysis indicates higher temperatures are consistently associated with diminishing lake areas, a trend commonly observed in water bodies. While annual precipitation also influences lake areas, the effect is less pronounced, with a correlation coefficient of 0.141, signifying a positive connection between the two variables. Temporal analysis reveals climate impact exhibits a one-year time lag, meaning changes in the current year’s climate manifest in alterations in lake areas in the subsequent year. Generalized Additive Models provide further insights, emphasizing the complex, non-linear nature of the relationship between climatic factors and lake areas. Pseudo-R2 values for lakes on the Kerch Peninsula range from 0.0913 to 0.2769, indicating the proportion of variability in lake area explained by the models. These values emphasize the significance of essential factors, though some unexplained variability remains. In summary, this research highlights the critical role of climate factors in shaping the dynamics of lakes in the Kerch Peninsula. The findings underscore the need for continued monitoring and adaptive management to address the multifaceted challenges posed by climate change and other contributing factors in this region.

ABSTRACTLake area derived from remote-sensing data is a primary data source, because changes in lake number and area are sensitive indicators of climate change. These indicators are especially useful when the climate change is not convoluted with a signal from direct anthropogenic activities. The data used for lake-area mapping is important, to avoid introducing unnecessary uncertainty into long-term trends of lake-area estimates. The methods for identifying waterbodies from satellite data are closely linked to the quality and efficiency of surface-water differentiation. However, few studies have comprehensively considered the factors affecting the selection of data and methods for mapping lake area in the Tibetan Plateau (TP), nor of evaluating their consequences. This study tests the dominant data sets (Landsat and Moderate Resolution Imaging Spectroradiometer (MODIS) data) and the methods for automated waterbody mapping on 14 large lakes (>500 km2) distributed across different climate zones of the TP. Seasonal changes in lake area and data availability from Landsat imagery are evaluated. Data obtained in October is optimal because in this month the lake area is relatively stable. The data window can be extended to September and November if insufficient data is available in October. Grouping data into three-year bins decreases the effects of year-to-year seasonal variability and provides a long-term trend that is suitable for time series analysis. The Landsat data (Multispectral Scanner, MSS; Thematic Mapper, TM; Enhanced Thematic Mapper Plus, ETM+; and Operational Land Imager, OLI) and MODIS data (MOD09A1) showed good performance for lake-area mapping. The Otsu method is used to determine the optimal threshold for distinguishing water from non-water features. Several water extraction indices, namely NDWIMcFeeters, NDWIXu, and AWEInon-shadow, yielded high overall classification accuracy (92%), kappa coefficient (0.83), and user’s accuracy (~90%) for lake-water classification using Landsat data. The MODIS data using NDWIMcFeeters and NDWIXu showed consistent lake area (r2 = 0.99) compared with Landsat data on the corresponding date with root mean square error (RMSE) values of 86.87 and 103.33 km2 and mean absolute error (MAE) values of 25.7 and 29.04 km2, respectively. The MODIS data is suitable for great lake mapping, which is the case for the large lakes in the TP. Although automated water extraction indices exhibited high accuracy in separating water from non-water, visual examination and manual editing are still necessary. Combined with recent Chinese high-resolution satellites, these remotely sensed imageries will provide a wealth of data for studies of lake dynamics and long-term lake evolution in the TP.

Ulanbuh Desert located in the ecological environment fragile areas of the monsoon margin, which is extremely sensitive to climate change. With the support of the temperature and precipitation data of the four meteorological stations in the distribution of Ulanbuh Desert margin over the nearly 60 years data, and by using the Mann-Kendall and the Mann-Whitney test, the mutation changes has analyzed. The results show that the temperature of the study area after its significant change in 1990 has been through a obvious warming process, and the average temperature from 1990 to 2010 was more than 1 °C higher than in 1955-1989. While there was a slight increase trend in the precipitation after its significant change in 1992, and the climate condition is generally warm and dry, so temporarily the conclusion that the climate condition will change to warm and wet is impossible.

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