Effects Of Precipitation Changes Research Articles

A Review of the Global Change Research on the Tibetan Plateau: From Field Observation to Manipulative Experiments

Global temperature increases and precipitation changes are both expected to alter alpine ecosystem structure and processes. In this paper, we reviewed the recent climate changes observed and the global change researches on the Tibetan Plateau. Firstly, we found that the mean annual temperature and precipitation (data from 75 meteorological stations, where all daily precipitation data are available) have increased since 1971, there were 0.5˚C and 0.7˚C per decade increase in annual and winter temperature, respectively, on Tibetan Plateau, and changes in precipitation were found both less spatially and temporally consistent. Secondly, we reviewed the climate change researches on the Tibetan Plateau published between 2000 and 2019 mainly focused on plant growth and ecosystem carbon balance which including plant phenology, plant productivity, plant diversity, exchanges in ecosystem carbon and soil organic carbon. Findings and insights from these studies have been very useful to understand how the alpine ecosystem processes respond to climate change. However, the effects of temperature increase on plant growth and ecosystem carbon balance are differ depending on the study sites and warming methods and periods, and the effects of precipitation changes are sparse.

Differential responses of soil bacteria and fungi to altered precipitation in a meadow steppe

Soil microorganisms are essential participants in ecosystem processes, yet their composition, diversity, and function are affected by altered precipitation. The patterns and key processes driving the effects of changes in precipitation on soil bacterial and fungal communities remain unclear. To better understand how changes in precipitation may affect soil microorganisms, we conducted a three-year field precipitation manipulation experiment, with treatments ranging from 50% reduction to 50% increases in precipitation, in a meadow steppe located in northeast China. Our results demonstrated that the bacterial community was more sensitive to changes in precipitation than the fungal community. The fungal community was sensitive to inter-annual differences in precipitation, but not to the treatment-induced changes in precipitation. Increased annual precipitation shifted the dominance of the microbial community from bacteria to fungi. Over the precipitation range (200–280 mm) soil microbial biomass and diversity are maximal, below the long-term mean annual precipitation (430 mm) for this site. Soil water content, pH, and total phosphorus were the main factors related to the variance in soil microbial community diversity. Results show non-linear, time-dependent, and interacting responses of bacterial and fungal biomass and diversity to soil properties under gradients of altered precipitation magnitude in this semi-arid grassland.

Assessing long-term spatio-temporal variability in humidity and drought in Iran using Pedj Drought Index (PDI)

Although drought is a normal feature of climate, there is confusion about its characteristics in both arid and semi-arid regions. This study investigated the effects of changes in precipitation and temperature on spatio-temporal drought and humidity variations throughout the diverse (principally arid- and semi-arid) climates of Iran during recent decades using the Pedj Drought Index (PDI). The standardized anomaly index (SAI) for annual precipitation (SAIPr) and mean temperature (SAITm) was calculated using their monthly records at sixteen meteorological stations scattered throughout Iran during 1951–2010. The results showed: (1) statistically significant (p < 0.05) drying trends in annual PDI values at most of the stations, primarily accompanied by substantial increases in annual SAITm; (2) considerable positive and negative relationships of annual PDI with annual SAITm and SAIPr, respectively; (3) the 1970s/2000s as the predominant humid/dry decade; (4) More frequent drought than humidity events at ~81% of stations; (5) the longest drought was 13 years (1998–2010) seen at the Kermanshah station, with the semi-dry climate in the west of Iran; and (6) the 2010 drought spatially extended over all the stations studied throughout the country. In conclusion, the PDI acceptably succeeded to characterize annual droughts in Iran previously captured by other prominent recommended drought indices.

Reviews and syntheses: Soil responses to manipulated precipitation changes – an assessment of meta-analyses

Abstract. In the face of ongoing and projected climatic changes, precipitation manipulation experiments (PMEs) have produced a wealth of data about the effects of precipitation changes on soils. In response, researchers have undertaken a number of synthetic efforts. Several meta-analyses have been conducted, each revealing new aspects of soil responses to precipitation changes. Here, we conducted a comparative analysis of the findings of 16 meta-analyses focused on the effects of precipitation changes on 42 soil response variables, covering a wide range of soil processes. We examine responses of individual variables as well as more integrative responses of carbon and nitrogen cycles. We find strong agreement among meta-analyses that belowground carbon and nitrogen cycling accelerate under increased precipitation and slow under decreased precipitation, while bacterial and fungal communities are relatively resistant to decreased precipitation. Much attention has been paid to fluxes and pools in carbon, nitrogen, and phosphorus cycles, such as gas emissions, soil carbon, soil phosphorus, extractable nitrogen ions, and biomass. The rates of processes underlying these variables (e.g., mineralization, fixation, and (de)nitrification) are less frequently covered in meta-analytic studies, with the major exception of respiration rates. Shifting scientific attention to these less broadly evaluated processes would deepen the current understanding of the effects of precipitation changes on soil and provide new insights. By jointly evaluating meta-analyses focused on a wide range of variables, we provide here a holistic view of soil responses to changes in precipitation.

Application and performance evaluation of time series, neural networks and HARTT models in predicting groundwater level changes, Najafabad Plain, Iran

In this study, the application and performance of three models, including artificial neural networks, HARTT model and time series models for predicting the groundwater level in Najafabad plain were evaluated. For this purpose, SPSS, MATLAB and HARTT software packages were used to construct and evaluate each of these methods. Different parameters were used as inputs to estimate the groundwater level in each of these models. The results showed that all three models are capable of estimating the groundwater level with relatively good accuracy. However, the accuracy of seasonal ARIMA models and neural networks is higher than that of the HARTT model, though the performances of the two models are relatively similar. Based on the goodness of fit results, the seasonal ARIMA models are more appropriate for groundwater level prediction, because of the lower error, but the seasonal ARIMA models require some assumptions on the errors that make the modeling difficult, while the artificial neural network models have no such problems. But artificial neural networks have some limitations, such as the lack of a comprehensive theory and the need for a large number of observations due to the nonlinear structure of the networks. In addition, neural network inputs, like coefficients of regression models, are not interpretable and act as a black-box model. Therefore, they are only suitable for prediction and are not applicable for analyzing and interpreting the effects of each parameter on the groundwater level. Also one of the benefits of ARIMA models is that it can be used for short-term groundwater level prediction without the need for input data. This is especially important for areas without observation data or areas where data are limited. Furthermore, the results show that in addition to the ability of groundwater level prediction, the HARTT model can predict the effects of precipitation changes on groundwater level and the time delay between precipitation and its effect on the groundwater level, which this delay for different wells, based on the different effective parameters, is different.

Environmental factors driving phytoplankton biomass and diversity in a tropical reservoir

We determined the spatial and temporal variation of phytoplankton biomass and diversity in 10 fortnightly sampling journeys verifying five sampling sites in El Peñol-Guatapé reservoir located in Antioquia, Colombia. In situ and ex situ physical and chemical variables were measured and phytoplankton samples were taken. Richness was dominated by Chlorophyta and biomass by Dinophyta. This variable was higher in the transition zone while in the riverine zone it showed average values, the lowest were registered in the lacustrine zone. Diversity was lower in the riverine zone, but it increased considerably in the transition zone and in the lacustrine zone where it showed similar values. At the vertical scale, biomass and diversity did not vary widely. Biomass showed a differential response to the effect of precipitation changes and water levels in the reservoir zones. Due to the low variability in environmental conditions, diversity was homogeneous time-wise. These results suggest that factors related to the hydrodynamic such as precipitation and water level resulting from the dam operation and inflow have a slight influence on the temporal variations of phytoplankton biomass and structure. There was a direct relationship between these attributes and physical variables such as turbidity and nutrients concentration at spatial scale while at the vertical scale, mixing patterns and the influence of the wind explained the absence of the vertical gradient of biomass and phytoplankton structure.

Soil responses to manipulated precipitation changes: A synthesis of meta-analyses

Abstract. In the face of ongoing and projected precipitation changes, precipitation manipulation experiments (PMEs) have produced a wealth of data about the effects of precipitation changes on soils. In response, researchers have undertaken a number of synthetic efforts. Several meta-analyses have been conducted, each revealing new aspects of soil responses to precipitation changes. We synthesize the findings of 16 meta-analyses focused on the effects of decreased and increased precipitation on 42 soil response variables, covering a wide range of soil processes and examining responses of individual variables as well as more integrative responses of carbon and nitrogen cycles. We found a strong agreement among meta-analyses that decreased and increased precipitation inhibits and promotes belowground carbon and nitrogen cycling, respectively, while microbial communities are relatively resistant to precipitation changes. Much attention has been paid to fluxes and pools in carbon, nitrogen, and phosphorus cycles, such as gas emissions, soil carbon, soil phosphorus, extractable nitrogen ions, and biomass, but the rates of processes underlying these variables are less frequently covered in meta-analytic studies (e.g., rates of mineralization, fixation, and de/nitrification). Shifting scientific attention to these “processes” would, therefore, deepen the current understanding of the effects of precipitation changes on soil and provide new insights. By comparing meta-analyses focused on different variables, we provide here a quantitative and holistic view of soil responses to changes in precipitation.

Effects of precipitation changes on soil bacterial community composition and diversity in the Junggar desert of Xinjiang, China.

Variation in precipitation can markedly affect the structure and function of soil microbial communities, especially in arid areas which are limited by water resources. Therefore, it is critical to understand how soil bacterial community composition and diversity will respond to variation in precipitation. In this study, we examined the soil bacterial community structure and diversity between five precipitation treatments (60% decrease, 30% decrease, control, 30% increase and 60% increase in precipitation) in the same arid site, in the Junggar desert of Xinjiang, northern China. The dominant bacterial phyla, present at similar frequencies in plots with different precipitation levels, were Actinobacteria, Proteobacteria, Bacteroidetes, Acidobacteria and Chloroflexi. The Shannon-Wiener and Chao1 indices of soil bacterial α-diversity were both positively correlated with plant diversity. Our results indicated that (1) extreme drought significantly decreased bacterial abundance and diversity compared with increased precipitation; (2) variation in precipitation did not change the dominant components of the bacterial communities; and (3) soil pH and total nitrogen concentration were the key factors affecting soil bacterial composition in the Junggar desert.

Assessment of Climate change parameters impact on long-term sediment transport trend Case study; Azam River basin

At the turn of the new decade, climate change is one of the key issues that has affected all social, economic and other human's activities. In this study, the effects of changes in precipitation and temperature parameters on sediment changes in the Azam River located in Yazd province of Iran were investigated. The Mann-Kendall test was used to identify the changes in sediment parameters. Subsequently, in order to predict the sediment changes the artificial neural network (ANN) was considered. In order to use the ANN model for predicting the sediment amount, firstly, the model was trained by temperature and precipitation data as input parameters, in the next step the ANN model sensitivity analysis was done by changing the layers and the neuron numbers, finally the most suitable model with 25 layers and 30 neurons was chosen. The final trained ANN model was used forecasting the sediment amount over 2015-2044.

Assessment of climate change parameters impact on long-term sediment transport trend case study: Azam River basin

At the turn of the new decade, climate change is one of the key issues that has affected all social, economic and other human's activities. In this study, the effects of changes in precipitation and temperature parameters on sediment changes in the Azam River located in Yazd province of Iran were investigated. The Mann-Kendall test was used to identify the changes in sediment parameters. Subsequently, in order to predict the sediment changes the artificial neural network (ANN) was considered. In order to use the ANN model for predicting the sediment amount, firstly, the model was trained by temperature and precipitation data as input parameters, in the next step the ANN model sensitivity analysis was done by changing the layers and the neuron numbers, finally the most suitable model with 25 layers and 30 neurons was chosen. The final trained ANN model was used forecasting the sediment amount over 2015-2044.

Spatiotemporal variation in leaf size and shape in response to climate

Abstract Aims Morphological variation of leaves is a key indicator of plant response to climatic change. Leaf size and shape are associated with carbon, water and energy exchange of plants with their environment. However, whether and how leaf size and shape responded to climate change over the past decades remains poorly studied. Moreover, many studies have only explored inter- but not intraspecific variation in leaf size and shape across space and time. Methods We collected &amp;gt;6000 herbarium specimens spanning 98 years (1910–2008) in China for seven representative dicot species and measured their leaf length and width. We explored geographical patterns and temporal trends in leaf size (i.e. leaf length, leaf width and length × width product) and shape (i.e. length/width ratio), and investigated the effects of changes in precipitation and temperature over time and space on the variation in leaf size and shape. Important Findings After accounting for the effects of sampling time, leaf size decreased with latitude for all species combined, but the relationship varied among species. Leaf size and shape were positively correlated with temperature and precipitation across space. After accounting for the effects of sampling locations, leaf size of all species combined increased with time. Leaf size changes over time were mostly positively correlated with precipitation, whereas leaf shape changes were mostly correlated with temperature. Overall, our results indicate significant spatial and temporal intraspecific variation in leaf size and shape in response to climate. Our study also demonstrates that herbarium specimens collected over a considerable period of time provide a good resource to study the impacts of climate change on plant morphological traits.

Rapid Pleistocene desiccation and the future of Africa's Lake Victoria

The effects of precipitation changes on tropical East African ecosystems and human populations is poorly understood due to the complex interplay between global and regional processes and missing data from key regions and time periods. We generate a water-budget model for Lake Victoria, the largest tropical lake in the world, the source of the White Nile, and a region that supports some of the densest human populations in Africa, that assesses the impact of changing climate on lake levels and the rate of lake level change. Model results demonstrate that significant changes in the size and volume of Lake Victoria are possible in response to changes in temperature, precipitation, and orbital forcing. This modeling indicates that Lake Victoria can transition back and forth between modern lake levels and complete desiccation in centuries to a few millennia, which is rapid enough to allow for two previously observed desiccation events between 14-18 ka, during which time the lake drained and refilled twice. Combined observations from modeling and estimates of paleoprecipitation indicate that Lake Victoria was likely desiccated between 94-36 ka. This dry interval partially overlaps the megadrought (140-70 ka) identified in Lakes Malawi and Tanganyika further south, and the cooler, drier conditions identified in the Gulf of Aden between 75-50 ka. This prolonged desiccation was probably driven by eccentricity-enhanced precession and high-latitude forcing that affected the Congo Air Boundary convergence. Using future climate projections, our model also predicts that at current rates of temperature change and previous rates of lake level fall, Lake Victoria could have no outlet to the White Nile within 10 years, and Kenya could lose access to the lake in <400 years, which would significantly affect the economic resources supplied by Lake Victoria to the East African Community.

Climate change, reforestation/afforestation, and urbanization impacts on evapotranspiration and streamflow in Europe

Abstract. Since the 1950s, Europe has undergone large shifts in climate and land cover. Previous assessments of past and future changes in evapotranspiration or streamflow have either focussed on land use/cover or climate contributions or on individual catchments under specific climate conditions, but not on all aspects at larger scales. Here, we aim to understand how decadal changes in climate (e.g. precipitation, temperature) and land use (e.g. deforestation/afforestation, urbanization) have impacted the amount and distribution of water resource availability (both evapotranspiration and streamflow) across Europe since the 1950s. To this end, we simulate the distribution of average evapotranspiration and streamflow at high resolution (1 km2) by combining (a) a steady-state Budyko model for water balance partitioning constrained by long-term (lysimeter) observations across different land use types, (b) a novel decadal high-resolution historical land use reconstruction, and (c) gridded observations of key meteorological variables. The continental-scale patterns in the simulations agree well with coarser-scale observation-based estimates of evapotranspiration and also with observed changes in streamflow from small basins across Europe. We find that strong shifts in the continental-scale patterns of evapotranspiration and streamflow have occurred between the period around 1960 and 2010. In much of central-western Europe, our results show an increase in evapotranspiration of the order of 5 %–15 % between 1955–1965 and 2005–2015, whereas much of the Scandinavian peninsula shows increases exceeding 15 %. The Iberian Peninsula and other parts of the Mediterranean show a decrease of the order of 5 %–15 %. A similar north–south gradient was found for changes in streamflow, although changes in central-western Europe were generally small. Strong decreases and increases exceeding 45 % were found in parts of the Iberian and Scandinavian peninsulas, respectively. In Sweden, for example, increased precipitation is a larger driver than large-scale reforestation and afforestation, leading to increases in both streamflow and evapotranspiration. In most of the Mediterranean, decreased precipitation combines with increased forest cover and potential evapotranspiration to reduce streamflow. In spite of considerable local- and regional-scale complexity, the response of net actual evapotranspiration to changes in land use, precipitation, and potential evaporation is remarkably uniform across Europe, increasing by ∼ 35–60 km3 yr−1, equivalent to the discharge of a large river. For streamflow, effects of changes in precipitation (∼ 95 km3 yr−1) dominate land use and potential evapotranspiration contributions (∼ 45–60 km3 yr−1). Locally, increased forest cover, forest stand age, and urbanization have led to significant decreases and increases in available streamflow, even in catchments that are considered to be near-natural.

Impacts of Hydrological Changes on Nutrient Transport From Diffuse Sources in a Rural River Basin, Western Japan

AbstractIncreased frequency of heavy rainfall caused by climate change may affect nutrient transport from forests and agricultural lands into downstream rivers. However, little information is available on how the effects of land cover on nutrient concentrations in the downstream rivers change depending on hydrological conditions. To elucidate this, we investigated the effects of changes in precipitation and river discharge on the relationship between river nutrient concentrations (total nitrogen, total phosphorus, nitrate, and phosphate) and land cover in eight subbasins of the Hii River basin, western Japan. We hypothesized that coniferous forests and agricultural lands including poorly managed ones, which require thinning and fertilizer management, respectively, contribute to increases in nutrient concentrations in downstream rivers during storms. Linear mixed‐effects model analyses based on 18‐year observation data were used for testing the hypothesis. Results revealed that the slopes of the multiple regression analysis between nutrient concentrations and coniferous and broad‐leaved forest area ratios were negative and decreased with increasing daily precipitation. This suggests that forests contributed to the dilution of river nutrient concentrations during storms regardless of whether they were coniferous or broad leaved. In contrast, the slope of regression between nutrient concentrations and agricultural area ratio revealed the opposite trend, indicating that even a small percentage of agricultural area makes a large contribution to increases in nutrient concentrations as precipitation increases. Our results imply that storm runoff in response to rainfall results in an elevated supply of nitrogen and phosphorus attached to arable soils to the river.

Effects of changes in precipitation on energy and water balance in a Eurasian meadow steppe

IntroductionWater such as precipitation is the most critical environment driver of ecosystem processes and functions in semi-arid regions. Frequency and intensity of drought and transient waterlogging are expected to increase in the meadow steppe in northeastern China. Using a 4-year dataset of eddy covariance flux measurements, ground measurements of biomass, phenology, and meteorological conditions, we investigated the changes in energy fluxes at multiple temporal scales and under different precipitation regimes.ResultsThe meadow steppe was latent heat (LE) dominated when soil water content was > 0.3 m3 m−3, but switched to sensible heat (H) dominated status when soil water content fell below 0.3 m3 m−3. LE dominated the energy exchange of the meadow grasslands on a yearly basis. Intensive precipitation had a profound impact on water-energy balance that could reduce the damages of drought by elevating deep soil moisture. The influence of LE on waterlogging depended on timing, with increased LE at the beginning of growing season and decreased LE after waterlogging. Spring and summer droughts resulted in different energy partitioning between latent and sensible heat energies, with spring drought dramatically decreased the LE fraction due to the change in water. In contrast, summer drought had little impact on LE due to the sufficient water input from large precipitation events at the beginning of the growing season.ConclusionsThere existed great seasonal and interannual variabilities in energy balance and partitioning in the meadow steppe over the 4-year study period, which were strongly influenced by changes in precipitation. The water loss through latent heat was more sensitive to spring drought than to summer drought, while summer drought had negligible impact on LE. Waterlogging contributed to LE by enhancing its values during and after the waterlogged periods at the beginning of the growing season in a dry year, but lowering its value after the waterlogged periods in growing season.

Effect of Precipitation Change on Dams Storage in Jordan

Precipitation patterns' change, rising surface temperature, extensive ice melting and increments in intensity and frequency of droughts and floods are several kinds of the reported hydrologic changes that are connected with the worldwide climate change. Therefore, climate change and its associated precipitation change are anticipated to influence the water storage as well as water supply in Jordan and impose challenges in front of the current water management policies and plans. The hydrological impacts of upcoming anticipated climate may influence the Jordanian dams' capacity and operating attributes. Accordingly, this paper tends to explore and review mainly the effect of precipitation change on dams' storage in Jordan, by providing a brief review of major types of dams and considerations that must be taken through their design and construction as well as clarifying the necessity for a national climate change policy for Jordan. The researcher concluded that climate change and precipitation variability require new management strategies for water storage infrastructures (reservoirs), including the design for new dams and rehabilitation of the infrastructure of aging dams as well as imposing new operational systems. Several advantages of dam management ought to be considered, evaluated and actualized right away in Jordan alongside with issuing of national climate change policy taking into account the effect of precipitation change. DOI : 10.7176/JEES/9-5-05 Publication date :May 31 st 2019

Effects of precipitation change on fine root morphology and dynamics at a global scale: a meta-analysis

We compiled data from 495 observations and 103 papers and carried out a meta-analysis of the responses of fine root biomass, production, decomposition, and morphology to precipitation increases and decreases. In addition, we evaluated the effects of plant life form, soil depth, and experiment duration on the responses of fine roots to precipitation changes. Our results confirmed that decreased precipitation limited fine root diameter and accelerated turnover. Increased precipitation stimulated fine root elongation and enhanced the fine root accumulation. The responses of fine roots to precipitation changes varied among plants of different life forms. Tree fine root production and decomposition and non-tree fine root diameter varied most strongly under decreased precipitation. Specific root length of non-tree fine roots was much higher than that of tree fine roots under increased precipitation. Decreased precipitation limited the growth of fine roots in 20–40 cm deep soil, whereas increased precipitation promoted the growth of fine roots in both shallow and deep soil layers. The responses of fine roots to decreased precipitation were affected by experiment duration. Results filled the gap of evaluation data on the effect of precipitation change on fine root morphology and dynamics, which are useful for better predicting the C cycle under precipitation change.

Cause Analysis of Groundwater Level Changes in a Seismic Monitoring Hole: A Case Study of Well Yu-11 in Kaifeng

Changes in groundwater levels provide important information for seismic monitoring and prediction, but groundwater-level changes can be caused by multiple factors that need to be analyzed carefully. In particular, the effects of changes in precipitation have masked information on activities internal to the Earth. It is therefore of great importance to effectively eliminate the influences of precipitation change on groundwater levels. Kaifeng Well Yu-11, whose water level has dropped remarkably in recent years, lies in a national earthquake key defense area. Based on daily well-water-level and precipitation data from Well Yu-11, this paper analyzes its water-level dynamics and precipitation variation characteristics using Pearson correlation and regression analysis methods. The results show that change in precipitation is not the cause of the abnormal drop in the water level of Well Yu-11.

降雨量改变对黄河三角洲滨海湿地土壤呼吸的影响

降雨量改变对黄河三角洲滨海湿地土壤呼吸的影响

Effect of changing vegetation and precipitation on denudation – Part 2: Predicted landscape response to transient climate and vegetation cover over millennial to million-year timescales

Abstract. We present a numerical modeling investigation into the interactions between transient climate and vegetation cover with hillslope and detachment limited fluvial processes. Model simulations were designed to investigate topographic patterns and behavior resulting from changing climate and the associated changes in surface vegetation cover. The Landlab surface process model was modified to evaluate the effects of temporal variations in vegetation cover on hillslope diffusion and fluvial erosion. A suite of simulations were conducted to represent present-day climatic conditions and satellite derived vegetation cover at four different research areas in the Chilean Coastal Cordillera. These simulations included steady-state simulations as well as transient simulations with forcings in either climate or vegetation cover over millennial to million-year timescales. Two different transient variations in climate and vegetation cover including a step change in climate or vegetation were used, as well as 100 kyr oscillations over 5 Myr. We conducted eight different step-change simulations for positive and negative perturbations in either vegetation cover or climate and six simulations with oscillating transient forcings for either vegetation cover, climate, or oscillations in both vegetation cover and climate. Results indicate that the coupled influence of surface vegetation cover and mean annual precipitation shifts basin landforms towards a new steady state, with the magnitude of the change being highly sensitive to the initial vegetation and climate conditions of the basin. Dry, non-vegetated basins show higher magnitudes of adjustment than basins that are situated in wetter conditions with higher vegetation cover. For coupled conditions when surface vegetation cover and mean annual precipitation change simultaneously, the landscape response tends to be weaker. When vegetation cover and mean annual precipitation change independently from one another, higher magnitude shifts in topographic metrics are predicted. Changes in vegetation cover show a higher impact on topography for low initial surface cover values; however, for areas with high initial surface cover, the effect of changes in precipitation dominate the formation of landscapes. This study demonstrates the sensitivity of catchment characteristics to different transient forcings in vegetation cover and mean annual precipitation, with initial vegetation and climate conditions playing a crucial role.