Hurricane Maria was associated with record‐breaking rainfall over Puerto Rico and caused unprecedented flooding and landslides. Here we analyze the extreme rainfall produced by Hurricane Maria using 35 stations with daily precipitation data from 1956–2016. A covariate‐based extreme value analysis point process approach that accounts for natural climate variability and long‐term climate change influences on extreme rainfall is applied. Hurricane Maria produced the single largest maximum rainfall event since 1956 and had the highest total averaged precipitation of 129 storms that have impacted the island since 1956. Return periods for an event of Hurricane Maria's precipitation magnitude decreased in 48.6% of stations across Puerto Rico and at least halved when averaged across the island. Within the most affected areas it is likely that the probability of precipitation of Maria's magnitude has increased by a factor greater than 1 (best estimate 4.85) as a result of long‐term climate trends.

Although tropical cyclone rainfall (TCR) is common over Puerto Rico, the factors that cause this rain to vary from one storm to another have not been studied. The aim of this article is to understand how storm‐specific characteristics including storm location, duration, storm centre proximity to land, intensity, horizontal translation speed (HTS) and environmental factors like moisture and vertical wind shear affect TCR variability over Puerto Rico. TCR was determined at rain gauge locations for days when storms were within a 500 km radius of Puerto Rico. The station data were then used to calculate an island‐averaged total rainfall value for 86 storms during 1970–2010. The maximum observed rainfall was also examined. Correlation analyses of the individual predictors, principal component regression (PCR) procedures and Mann–Whitney U tests identified precipitable water, storm centre proximity to land, mid‐level relative humidity (MRH), duration, HTS and longitude as the predictors with the strongest influence on rainfall. The PCR showed that a component comprised of precipitable water, MRH and longitude accounted for more than 60% in TCR variability. When an additional component comprised of storm duration, storm centre proximity to land and translation speed was considered, the PCR model explained 70% (52%) of the variability in mean (maximum) TCR. Key threshold values for high rainfall across Puerto Rico are a storm centre distance of 233 km or less and moisture exceeding 44.5 mm of precipitable water and 44.5% of relative humidity with forward speeds of 6.4 m s⁻¹ or less. Extreme rainfall at a single location can occur when a TC's centre is over 450 km away.

In recent years, California has experienced wildfire seasons of increasing frequency and magnitude, especially in terms of wildfire burned areas. Here, we investigate the precipitation and vegetation growth preceding each wildfire season for the 2001–2020 period to determine if antecedent rainfall led to enhanced vegetation growth in wildfire burned areas in California. Precipitation data from the Global Precipitation Measurement (GPM) Mission and Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI) data are examined to determine if antecedent rainfall and vegetation were normal, above, or below average, for the peak wet (December–February) and peak growth (March–May) periods preceding each wildfire season, as well as for the two previous wet and growth seasons. Then spatial correlations are done between precipitation and the vegetation indexes to determine the statistical significance of the relationships. Eleven of the 20 wildfire seasons were generally found to be preceded by above average levels of precipitation and vegetation growth. In three of the six seasons with more wildfire activities, linear regression model results show high positive correlations between precipitation and vegetation, suggesting that antecedent rainfall fueled vegetation growth that might have caused a significant impact on wildfire burned areas. Most of the larger wildfires in California, including the largest on record, exhibited positive correlations between antecedent rainfall and vegetation. Our results suggest that antecedent rainfall in California led to enhanced vegetation growth that later fueled more than half of the wildfire seasons analyzed in this study.

This study explores two different tropical cyclone rainfall (TCR) problems: first, the identification of areas where TCR is highly concentrated and, second, the contribution of tropical cyclones (TCs) to the climatology of Puerto Rico for the period 1970–2010. A total of 86 storms within a 500-km radius of Puerto Rico were analyzed. Daily and monthly rainfall data from 32 weather stations were used to generate interpolated surfaces. Two geostatistical interpolation techniques were implemented: ordinary kriging and ordinary cokriging. Results show that rainfall from most TCs tends to be clustered in the eastern, southeastern, and central regions of the island, with a decrease in values toward the west. TCs closer to Puerto Rico (≤230 km) and embedded in high moisture environments (≥44.5 mm) exhibited the highest rainfall values, with most concentrated in the high elevation areas of the southeastern region of the island. Months with the largest TC contributions to rainfall (20–30%) were August and September, while the lowest contributions were found in June and November. For August, stations in the southern and eastern portions of the island had TCR contributions of >20%, with some stations in the southern coastal plains exhibiting 30%.