The water vapor transport and moisture budget over eastern China remotely forced by the cold-tongue (CT) and warm-pool (WP) El Niño show striking differences throughout their lifetime. The water vapor transport response is weak in the developing summer but strong in the remaining phases of CT El Niño, whereas the opposite occurs during WP El Niño. WP El Niño causes a moisture deficit over the Yangtze River valley (YZ) in the developing summer and over southeastern China (SE) in the developing fall, whereas CT El Niño induces a moisture surplus first over SE during the developing fall with the influential area expanding in the decaying spring and shifting northward in the decaying summer. It is the divergence of meridional water vapor transport that dominates the total water vapor divergence anomaly, with the divergence of zonal transport showing an opposite pattern with smaller magnitude. Investigation of the vertical profile of moisture budget shows a great baroclinicity, with the strongest abnormal moisture budget occurring in different levels. The moisture transport via the southern boundary plays a crucial role in the regional moisture budget anomalies and is located near the surface over SE, in the lower troposphere over the YZ, and at the lower-middle troposphere over the eastern part of northern China. The enhanced moisture surplus near the surface forced by WP El Niño over SE in the mature winter and decaying spring is offset by a moisture deficit within the lower-middle troposphere due to a diverse response circulation at different vertical levels.

A combination of Ward’s and k-means clustering was applied to a 3-month standardized precipitation index (SPI-03), and eight divisions of homogeneous drought variation throughout China were identified from the perspective of meteorological and agricultural droughts. A greater meridional gradient appeared over eastern China (six divisions) than over western China (two divisions). The climate division facilitated the evaluating of not only regional but also widespread droughts. Trend evaluation showed that western north China (WNC) has become increasingly wet in recent decades, while northern northeast China (NNE) has become increasingly dry. The Yangtze River valley (YZ) tended to experience less and weaker drought after the late 1970s. Southern northeast China (SNE) and the southwestern China–Tibetan Plateau (SW-TP) showed a decreasing trend in long-term but not short-term SPIs, implying that long-term drought conditions might develop continuously, thus allowing the following droughts to develop more rapidly and with a stronger intensity. Examination of the drought risk under El Niño revealed that northern regions were likely to suffer from drought rather than flood in the developing phase and the reverse in the decaying phase. Southeastern China (SE) and the YZ were vulnerable to flood rather than drought in the mature and decaying spring, with SE subjected to drought in the decaying summer. Such a distinctive regional pattern of drought risks was closely connected with the abnormal moisture supply patterns modulated by ENSO in different phases.

The Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), which incorporates satellite imagery and in situ station information, is a new high-resolution long-term precipitation dataset available since 1981. This study aims to understand the performance of the latest version of CHIRPS in depicting the multiple timescale precipitation variation over Taiwan. The analysis is focused on examining whether CHIRPS is better than another satellite precipitation product—the Integrated Multi-satellitE Retrievals for Global Precipitation Mission (GPM) final run (hereafter IMERG)—which is known to effectively capture the precipitation variation over Taiwan. We carried out the evaluations made for annual cycle, seasonal cycle, interannual variation, and daily variation during 2001–2019. Our results show that IMERG is slightly better than CHIRPS considering most of the features examined; however, CHIRPS performs better than that of IMERG in representing the (1) magnitude of the annual cycle of monthly precipitation climatology, (2) spatial distribution of the seasonal mean precipitation for all four seasons, (3) quantitative precipitation estimation of the interannual variation of area-averaged winter precipitation in Taiwan, and (4) occurrence frequency of the non-rainy grids in winter. Notably, despite the fact that CHIRPS is not better than IMERG for many examined features, CHIRPS can depict the temporal variation in precipitation over Taiwan on annual, seasonal, and interannual timescales with 95% significance. This highlights the potential use of CHIRPS in studying the multiple timescale variation in precipitation over Taiwan during the years 1981–2000, for which there are no data available in the IMERG database.

The summer moisture circulation anomaly over East Asia and the western North Pacific (WNP) couples well with the El Niño–Southern Oscillation (ENSO) in a quasi-4-yr period. The moisture circulation is dominated by two well-separated modes. The first mode exhibits an anticyclonic (cyclonic) moisture circulation over tropical–subtropical East Asia–WNP with an easterly (westerly) transport over the tropical WNP–Indian Ocean; the second mode displays an alternating pattern with an anticyclonic (cyclonic) moisture circulation over the subtropical WNP layered between two cyclonic (anticyclonic) circulations. Both modes couple well with the ENSO signal during its quasi-4-yr cycle. Within the cycle, in the summer of a developing warm episode, the positive phase of the second mode plays a key role, while in the transitional summer between a decaying warm episode and a developing cool episode, the positive phase of the first mode tends to take effect. In the summer of a developing cool episode, the negative phase of the second mode plays an important role, while the negative phase of the first mode tends to take effect in the transitional summer between a decaying cool episode and a developing warm episode. The anticyclone (cyclone) over the Philippine Sea region serves as a bridge in the quasi-four-year coupling. Its establishment and eastward extension modify moisture circulation over East Asia–WNP. Conversely, the easterly (westerly) wind to the south of the anticyclone (cyclone) is beneficial for the formation and eastward propagation of the Kelvin wave and, hence, to the development of the quasi-4-yr periodic ENSO episode.

The variation in regional precipitation over southeast and southwest China depends strongly on externally imported moisture rather than local evaporation. Associated with the different climate over the two regions, great discrepancies appear in the annual cycles of the moisture supply. Stationary moisture transport dominates externally imported moisture to a large extent, with transient transport being much weaker. The stationary moisture sink over southeast China is strong during spring and summer due to strong moisture input via the southern boundary and weak during fall and winter due to the offset between the output via the southern boundary and the net zonal boundary atmospheric flux. Zonal stationary moisture transport dominates the variation in moisture supply over southwest China. Negative net zonal boundary atmospheric flux countervails (collaborates) with positive meridional transport during the dry (wet) season. Stationary moisture circulations dominate regional atmospheric moisture convergence anomalies over both southeast and southwest China. Weak cold air activity is favorable for a strong moisture sink over southeast China, while the reverse appears over southwest China in spring. The east-to-west location of the abnormal anticyclone determines whether strong moisture converges over southeast China or southwest China in fall. The anticyclonic circulation anomaly over the Philippine Sea, remotely forced by El Niño, is crucial to the strong moisture sink over southeast China from winter to spring, while it does not play a role in the abnormal moisture sink over southwest China.