Analysis of Annual Trends in Mean and Extreme Temperature and Precipitation Events in Haiti over the Last Four Decades, 1981–2020

Extreme weather events have increasingly disrupted Haiti’s socio-economic development. This study assesses long-term trends in mean and extreme temperature, precipitation, and near-surface humidity indices across Haiti for 1981–2020, using ERA5-Land temperature and humidity fields together with Multi-Source Weighted-Ensemble Precipitation (MSWEP), both at 0.1° resolution. Trends were quantified with the Theil–Sen estimator and tested with Mann–Kendall (MK) after Trend-Free Pre-Whitening (TFPW). Warm days (TX90p, percentage of days when daily maximum temperature exceeds the 90th percentile of the reference period) and warm nights (TN90p, percentage of days when daily minimum temperature exceeds the 90th percentile) increase nationwide by about 12 and 20 additional days per decade, while mean maximum and minimum temperatures warm by 0.17 °C and 0.22 °C per decade, respectively. Nocturnal warming is accompanied by a significant rise in near-surface water vapor pressure (+0.15 hPa per decade), whose detrended interannual variability correlates strongly with TN90p (r = 0.59), identifying the water-vapor greenhouse effect as a key driver of the faster warming of nights than days. Precipitation shows no significant national trend, except for very wet days (R90p, percentage of days with precipitation above the 90th percentile of wet days, +2.18% per decade) and a decline in rainy days (RR1, number of days with precipitation ≥ 1 mm, –4 days per decade). These results provide the first country-wide baseline of temperature and precipitation extremes for climate-risk assessment in Haiti.