Climatic change in southern Kazakhstan since 1850 C.E. inferred from tree rings

Integrated nexus approach to assessing climate change impacts on grassland ecosystem dynamics: A case study of the grasslands in Tanzania

This study addresses the intricate interplay between climate, vegetation, and livestock dynamics in Tanzania within the Climate-Vegetation-Livestock (CVL) nexus through a quantitative assessment. By examining the temporal and spatial relationships between vegetation indices (NDVI, EVI, NPP) and key climatic variables (Precipitation, Temperature, Evapotranspiration) from 2009 to 2019, and projecting to 2050, this research aims to elucidate vegetation responses to climate change and its subsequent impacts on livestock. To this end, the relationship between the vegetation dynamics indicators (NDVI, NPP) and climate parameters is evaluated to quantify the vegetation response to climate change using statistical models. Next, an examination of multicollinearity is conducted to investigate potential interactions (nexus) between variables, incorporating the correlation among independent variables. Notably, the evaluation of performance and accuracy for the mentioned models is conducted through the cross-validation method and validation indices. Ultimately, the variation between projected NPP and NDVI (average for 2040-2060) and the present NPP and NDVI (average for 2009-2020) identifies the regions that are most likely susceptible, showcasing the vegetation cover's reaction to climate change in different emission scenarios. The results unveil significant spatio-temporal variations in vegetation dynamics influenced by climatic factors, where higher precipitation and temperatures correlate with increased vegetation health and productivity. The projected fluctuations in NDVI and NPP values indicate varying trends across different regions, with a general decrease in vegetation density and productivity from the northeast to the west under both RCP2.6 and RCP8.5 scenarios by 2050. This decline is attributed to anticipated changes in precipitation and temperature patterns driven by climate change. Furthermore, significant declines in vegetation density and productivity under emission scenarios, particularly in the southern regions compared to the present, suggest greater vulnerability to climate change impacts. This highlights the need for targeted mitigation strategies in these vulnerable areas. Meanwhile, northeast areas under both NDVI and NPP will remain unchanged across both climate scenarios. Moreover, analysis of livestock distribution maps indicates areas of vulnerability under climate change scenarios, with implications for future livestock management and agricultural practices. These findings underscore the importance of proactive planning and targeted interventions to enhance resilience and sustainable development in vulnerable regions, emphasizing the need for integrated approaches that consider the complex interactions between climate, vegetation, and livestock dynamics.

The Western Himalayan fir tree ring record of soil moisture in Pakistan since 1855

Data on historical soil moisture is crucial for assessing and responding to droughts that commonly occur in climate change-affected countries. The Himalayan temperate forests in Pakistan are particularly at risk of climate change. Developing nations lack the means to gather surface soil moisture (SSM) information. Tree rings are one way to bridge this gap. Here, we employed dendrochronological methods on climate-sensitive tree rings from Abies pindrow to reconstruct the SSM in the Western Himalayan mountain region of Pakistan from 1855 to 2020. December (r = 0.41), May (r = 0.40), and June (r = 0.65) SSMs were found to be the limiting factors for A. pindrow growth. However, only the June SSM showed reconstruction possibility (coefficient of efficiency = 0.201 and reduction of error = 0.325). Over the studied period, we found 6 years (wet year) when June SSM was above the threshold of 32.04 (mean + 2 δ) and 1 year (dry year) when June SSM was below the threshold of 21.28 (mean - 2 δ). It was revealed that 1921 and 1917 were the driest and wettest SSM of all time, with means of 19.34 and 36.49, respectively. Our study shows that winter soil moisture is critical for the growing season in the context of climate change. Climate change has broad impacts on tree growth in the Western Himalayas. This study will assist various stakeholders in understanding and managing local and regional climate change.

Variability in the minimum temperature over two centuries in the overlap region between the fringe of the Asian westerly region and the temperate continental-monsoon climate transition zone

The overlap region between the eastern fringe of the Asian westerly region and the temperate continental-monsoon climate transition zone is sensitive to climate changes and is characterized by fragile ecosystems. Uncovering the long-term historical climate variability patterns in this region is necessary. A standardized tree-ring width chronology was constructed based on the tree-ring samples collected from four representative tree species in four typical areas in the overlap region, and the 203- to 343-year annual mean minimum temperature series in the overlap region were reconstructed. The reconstructed series overlapped well with extreme climate events and low-temperature periods recorded in historical data. Therefore, the reconstructed model is stable and reliable. As suggested by the reconstructed series, the annual average minimum temperature in the overlap region changes sharply from east to west, and the periodicity change in the overlap region shows a trend of gradually weakening from the east and west ends to the middle. In the nineteenth century, the high-latitude area was in the high-temperature period, and the entire overlap region experienced significant low-temperature periods lasting 20-45 years until the 1950s. The western part had an earlier low-temperature period start time, a longer cooling duration, and a slower cooling rate than the central part. The overlap region experienced a significant warming period in approximately the last half-century, with temperatures increasing faster in the western and eastern parts than in the central part. The temperature variability in the overlap region was more intense in the last two centuries, with shorter periodicities and a larger proportion of cold periods. The central and western parts of the Asian westerly region, the mid- to high-latitude regions of the transition zone, and the overlap region experienced significant low-temperature periods or drastic cooling trends (the Little Ice Age) in the first half of the nineteenth century and significant warming trends afterwards due to global warming. The influences of these changes may have been exacerbated by the westerly circulation. The results of this study provide new insights into the use of dendroclimatology to extract temperature series in the Asian westerly region and the transition zone and a reference for research on global climate change.

Reconstruction of Hydrometeorological Data Using Dendrochronology and Machine Learning Approaches to Bias-Correct Climate Models in Northern Tien Shan, Kyrgyzstan

Tree-ring-width chronologies for 33 samples of Picea abies (L.) Karst. were developed, and a relationship between tree growth and hydrometeorological features was established and analyzed. Precipitation, temperature, and discharge records were extrapolated to understand past climate trends to evaluate the accuracy of global climate models (GCMs). Using Machine Learning (ML) approaches, hydrometeorological records were reconstructed/extrapolated back to 1886. An increase in the mean annual temperature (Tmeana) increased the mean annual discharge (Dmeana) via glacier melting; however, no temporal trends in annual precipitation were detected. For these reconstructed climate data, root-mean-square error (RMSE), Taylor diagrams, and Kling–Gupta efficiency (KGE) were used to evaluate and assess the robustness of GCMs. The CORDEX REMO models indicated the best performance for simulating precipitation and temperature over northern Tien Shan; these models replicated historical Tmena and Pa quite well (KGE = 0.24 and KGE = 0.24, respectively). Moreover, the multi-model ensembles with selected GCMs and bias correction can significantly increase the performance of climate models, especially for mountains region where small-scale orographic effects abound.

Spatiotemporal nexus between vegetation change and extreme climatic indices and their possible causes of change

Climate extremes have a significant impact on vegetation. However, little is known about vegetation response to climatic extremes in Bangladesh. The association of Normalized Difference Vegetation Index (NDVI) with nine extreme precipitation and temperature indices was evaluated to identify the nexus between vegetation and climatic extremes and their associations in Bangladesh for the period 1986-2017. Moreover, detrended fluctuation analysis (DFA) and Morlet wavelet analysis (MWA) were employed to evaluate the possible future trends and decipher the existing periodic cycles, respectively in the time series of NDVI and climate extremes. Besides, atmospheric variables of ECMWF ERA5 were used to examine the casual circulation mechanism responsible for climatic extremes of Bangladesh. The results revealed that the monthly NDVI is positively associated with extreme rainfall with spatiotemporal heterogeneity. Warm temperature indices showed a significant negative association with NDVI on the seasonal scale, while precipitation and cold temperature extremes showed a positive association with yearly NDVI. The DEA revealed a continuous increase in temperature extreme in the future, while no change in precipitation extremes. NDVI also revealed a significant association with extreme temperature indices with a time lag of one month and with precipitation extreme without time lag. Spatial analysis indicated insensitivity of marshy vegetation type to climate extremes in winter. The study revealed that elevated summer geopotential height, no visible anticyclonic center, reduced high cloud cover, and low solar radiation with higher humidity contributed to climatic extremes in Bangladesh. The nexus between NDVI and climatic extremes established in this study indicated that increasing warm temperature extremes due to global warming might have severe implications on Bangladesh's ecology and the environment in the future.