Abstract
Understanding the evolution and propagation of different drought types is crucial to reduce drought hazards in arid and semiarid regions. Here, Standardized Precipitation Index (SPI), Streamflow Drought Index (SDI), and Vegetation Condition Index (VCI) were used to investigate the spatiotemporal variation of different drought types and correlations between Pre (Pre-R)/post (Pos-R)-reservoir. Results showed that the average peak/intensity/duration/severity of meteorological droughts (MD) were greater in the Pre-R than in the Pos-R period in the upstream Heihe River Basin (UHRB), while there was little change between the Pre-R and Pos-R periods in the midstream Heihe River Basin (MHRB). The average peak/intensity/duration/severity of hydrological drought (HD) decreased in the mainstream for Yingluoxia (Ylx) but increased for Zhengyixia (Zyx) station in the Pos-R period. Propagation time decreased by 3 months (negative effect) in Ylx and increased by 8 months (positive effect) in Zyx compared with the Pre-R period. In the Pos-R period, propagation time increased (1–3 months) for tributaries (positive effect). Propagation times for the mainstream and tributaries varied for different seasons and time periods. Pearson’s correlation coefficient values were lower at short timescales (1–3 months) but higher at long timescales for the Pos-R period in Ylx and Zyx for SDI-1 with different timescales of SPI. The SDI and SPI had no lag in the UHRB and MHRB. However, VCI with SPI had a significant lag correlation at short timescales in the UHRB (lag 6 months) and MHRB (lag 4 months), and the VCI with SDI had a significant lag correlation for 1 month in the MHRB. The propagation time from MD to HD has been reduced for Pos-R in the UHRB. There was a positive effect (prolonged MD propagation HD time) in Pos-R but still faces serious drought stress in the MHRB.
Highlights
Drought is recognized as the world’s most costly and pressing natural hazard, giving rise to significant losses in the fields of the economy, ecology, and environment [1,2,3,4]. e damage from droughts is expected to increase in severity [5]
Meteorological droughts (MD) and Hydrological droughts (HD) for the Mainstream Characteristics between Different Timescales and resholds. e distribution of drought characteristics based on thresholds of −1, −1.5, and −2 for different timescales at different periods, including Pre-R (1965–abrupt change year), Pos-R, and total period (1965–2012), was evaluated in the upstream Heihe River Basin (UHRB) and midstream Heihe River Basin (MHRB) using boxplots. e drought characteristics of Standardized Precipitation Index (SPI)-1 and Streamflow Drought Index (SDI)-1 in the MHRB (Table S1) were almost consistent compared with historical records and, for different combinations of timescales, thresholds and periods (Table S2) are shown in the supporting information. e drought peak and intensity (Figures S1-S2), duration, and severity for different timescales at different thresholds are shown in Figure 3 for MD and in Figure 4 for HD
For MD, the average intensity, duration, and severity of fluctuations increased with cumulative timescale increases between Pre-R and Pos-R periods. e changes were more obvious in Pos-R compared with Pre-R periods for all thresholds in the UHRB. e average peak, intensity, duration, and severity of the MD did not change much for Pre-R, whereas Pos-R fluctuations
Summary
Drought is recognized as the world’s most costly and pressing natural hazard, giving rise to significant losses in the fields of the economy, ecology, and environment (e.g., crop losses, degradation and desertification, urban water supply shortages, and forest fires) [1,2,3,4]. e damage from droughts is expected to increase in severity [5]. Compared with other natural hazards, the spatial extent of drought is very large and its time of influence is commonly much longer. Drought can be classified into four types: meteorological, hydrological, agricultural, and socioeconomic [13]. Meteorological droughts (MD) are the water shortages caused by an imbalance in precipitation and evaporation; precipitation is commonly used for MD analysis [14, 15]. E Normalized Difference Vegetation Index (NDVI) is a good measure to estimate green biomass, leaf area index, and patterns of productivity and has been widely used to assess vegetation degradation, ecosystem features, and the physiological drought conditions of vegetation [20, 21] Because the influence of drought on terrestrial ecosystems is becoming increasingly acute, the vegetation response to drought is a crucial topic in the Advances in Meteorology domain of climate research [17,18,19]. e Normalized Difference Vegetation Index (NDVI) is a good measure to estimate green biomass, leaf area index, and patterns of productivity and has been widely used to assess vegetation degradation, ecosystem features, and the physiological drought conditions of vegetation [20, 21]
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