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.

中文翻译：

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黑河流域的气象干旱，水文干旱和NDVI：演变与传播

了解不同干旱类型的演变和传播对减少干旱和半干旱地区的干旱危害至关重要。在这里，使用标准降水指数（SPI），水流干旱指数（SDI）和植被状况指数（VCI）来调查不同干旱类型的时空变化以及Pre（Pre-R）/ post（Pos-R）之间的相关性-水库。结果表明，黑河流域上游（UHRB）Pre-R的平均干旱高峰/强度/持续时间/严重程度高于Pos-R时期，而Pre-R之间变化不大黑河中游（MHRB）的-R和Pos-R时期。在Pos-R时期，英罗峡（Ylx）的主流水文干旱（HD）的平均峰值/强度/持续时间/严重性降低，而正一峡（Zyx）站的平均峰值/强度/持续时间/严重性升高。与Pre-R时期相比，Ylx的传播时间减少了3个月（负面影响），Zyx的传播时间增加了8个月（正面影响）。在Pos-R时期，支流的传播时间增加（1-3个月）（正效应）。主流和支流的传播时间因季节和时间的不同而不同。对于SPI的不同时标，Sl-1在Ylx和Zyx的Pos-R期间，Pearson的相关系数值在较短的时间段（1-3个月）较低，但在较长的时间段较高。SDI和SPI在UHRB和MHRB中没有滞后。然而，在UHRB（滞后6个月）和MHRB（滞后4个月）中，带有SPI的VCI在短时间尺度上具有显着的滞后关联，而在MHRB中，具有SDI的VCI在1个月内具有显着的滞后关联。对于UHRB中的Pos-R，从MD到HD的传播时间已缩短。Pos-R具有积极作用（延长MD传播高清时间），但MHRB仍面临严重的干旱胁迫。