Predicting the dust events frequency around a degraded ecosystem and determining the contribution of their controlling factors using gradient boosting-based approaches and game theory

Meteorological drought migration characteristics based on an improved spatiotemporal structure approach in the Loess Plateau of China

The development of drought has spatial and temporal synchronization. Previous studies usually explore the spatial and temporal evolution of drought separately. Moreover, existing approaches are based on a fixed overlapping area and do not consider the variable drought cluster area during development. This study proposes an improved and simple approach to derive dynamic overlapping area threshold for 3-dimensional droughts extraction. Based on the one monthly Nonparametric Standardized Precipitation Index (NSPI), this improved approach was applied for investigating the migration characteristics of meteorological drought events in the Loess Plateau of China. Then, Random Forest and Extreme Gradient Boosting model with Shapley additive explanation values were used to quantify the importance of driving factors on the dynamics of drought characteristics. The results showed that: (1) the improved approach has a better performance on identifying prolonged droughts than the method using a fixed overlap area threshold; (2) spatially, meteorological drought events with high severity (DS), long duration (DD), large effected area (DA) and fast migration velocity (DV) mainly occur in the central region; (3) temporally, droughts are expected to aggravate with significantly increased DS and DA which are mainly caused by increased temperature and vegetation; and (4) meteorological droughts have a preferred westward migration direction and three dominant migration paths, which are crucial for local drought prevention and control. The findings of this study provide new perspectives on drought migration characteristics, which are important for the exploration of drought-driven mechanisms, risk assessment and future prediction.

Precipitation and vegetation transpiration variations dominate the dynamics of agricultural drought characteristics in China

Agricultural drought posing a significant threat to agricultural production is subject to the complex influence of ocean, terrestrial and meteorological multi-factors. Nevertheless, which factor dominating the dynamics of agricultural drought characteristics and their dynamic impact remain equivocal. To address this knowledge gap, we used ERA5 soil moisture to calculate the standardized soil moisture index (SSI) to characterize agricultural drought. The extreme gradient boosting model was then adopted to fully examine the influence of ocean, terrestrial and meteorological multi-factors on agricultural drought characteristics and their dynamics in China. Meanwhile, the Shapley additive explanation values were introduced to quantify the contribution of multiple drivers to drought characteristics. Our analysis reveals that the drought frequency, severity and duration in China ranged from 5-70, 2.15-35.02 and 1.76-31.20, respectively. Drought duration is increasing and drought intensity is intensifying in southeast, north and northwest China. In addition, potential evapotranspiration is the most significant driver of drought characteristics at the basin scale. Regarding the dynamic evolution of drought characteristics, the percentages of raster points for drought duration and severity with evapotranspiration as the dominant factor are 30.7 % and 32.7 %, and the percentages with precipitation are 35.3 % and 35.0 %, respectively. Precipitation in northern regions has a positive effect on decreasing drought characteristics, while in southern regions, evapotranspiration dominates the dynamics in drought characteristics due to increasing vegetation transpiration. Moreover, the drought severity is exacerbated by the Atlantic Multidecadal Oscillation in the Yangtze and Pearl River basins, while the contribution of the North Atlantic Oscillation to the drought duration evolution is increasing in the Yangtze River basin. Generally, this study sheds new insights into agricultural drought evolution and driving mechanism, which are beneficial for agricultural drought early warning and mitigation.

The Relationship Between Dust Sources and Airborne Bacteria in the Southwest of Iran

The biological agents are carried from deserts and dried lands to long distances by high dust volumes. Their adverse effects can be reduced by specifying and controlling dust sources and their related biological agents. Thus, the current work examined the relationship between the bacteria in air and soil samples by taking samples from the soil surface of two dust sources, as well as from air samples during spring from Khorramshahr and Abadan cities. The dust event is the most influential factor on airborne bacteria. There is an insignificant negative (-0.06), insignificant positive (0.14), and weak positive (0.24) correlation between airborne bacteria and UV radiation, relative humidity, and temperature, respectively. After preparing a 16S ribosomal DNA (rDNA) clone library from the soil and air samples, operational taxonomic unit picking and taxonomic assignment were conducted using QIIME Virtual Box. In the present work, Bacillus was the dominant species. The relationship between dust sources and air samples was determined by principal component analysis. Bacteria in the Hoor-Al-Azim dust source and airborne bacteria on dusty and non-dusty days showed a more significant correlation compared to bacteria in the Shadegan dust source. Source Tracker software was used to estimate the contribution of dust sources. The primary source of dust was associated with the dried areas of Hoor-Al-Azim on the non-dusty and dusty days. Finally, the long transport of airborne bacteria was assessed by moderate resolution imaging spectroradiometer (MODIS) and the back trajectory model of Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) data. The research findings can help decision-makers prioritize dust sources to control the adverse effects of dust.