Meta-analysis of the correlation between vegetation and precipitation in the temperate deserts of the Northern Hemisphere over the last 40 years

Temperate desert vegetation (TDV) is subjected to long-term seasonal or intermittent water stress, and precipitation is the main water source for desert vegetation. However, due to the limitations of existing research methods, data resources and spatiotemporal differences, universal conclusions and benchmark references at large spatial scales under the background of climate warming have been lacking in recent decades. In a systematic review, we evaluated primary studies and comprehensively analyzed the pooled correlation (pooled r (Pr)) between precipitation and TDV (P-TDV) in the Northern Hemisphere (NH) over the past 40 years by using a meta-analysis method to explore the monthly scale response pattern and heterogeneity pattern and to reveal the key TDV growth period under drought stress at a large spatial scale. The results showed the following. (1) In the mean state, the correlation between precipitation and TDV was at a moderate level in the NH over the last 40 years (Pr = 0.31). The spring Pr value was lowest, and the results were nonsignificant (p > 0.05). The highest Pr value was 0.40, and this value appeared in summer, followed by a value of 0.22 in autumn; the strongest relationship was found in June (Pr = 0.56). (2) The Pr values of TDV and precipitation with 1-and 2-month lag times were 0.34 and 0.31, respectively; these values were higher than those derived using lag times longer than 2 months. The statistical results were all significant and reflected a moderate correlation level. The above conclusions showed that TDV growth has the strongest demand for water in June and that spring drought conditions may have been one of the main stress factors affecting the growth of desert vegetation at the intra-annual scale in the northern temperate zone over the past 40 years.