Fig. 1: Precipitation seasonality and dry season defined as P < \(\bar{P}\).

a The mean ratio of P amplitudes of the harmonics at frequencies of two and one cycle per year via Fourier Analysis of whole daily time series (1983–2016) for each grid box based on the eight precipitation datasets. The blue line marks the boundaries with the ratio of 0.75, inside which grid boxes have two wet seasons and two dry seasons per year. b, c Daily mean rainfall (light blue) for each day of the year, smoothed using a 30-day running window (blue), the multi-year average daily mean precipitation (red horizontal line), and cumulative P anomaly value (green) for the grid box centered at 11.125°S, 57.875°W (left, point 1 in a) and 1.375°N, 12.875°E (right, point 2 in a) according to the daily CHIRPS precipitation dataset for the period 1983–2016 (see Eq. 3). Red dots mark the arrival of dry seasons (DSA), while blue dots mark the end of dry seasons (DSE). The solid black shaded area represents the water deficit, calculated as the cumulative difference between P and \(\bar{P}\) during the dry season. The two longest seasons are assumed to be the two seasons of interest for the biannual region (c). Similar patterns and definitions for P < Ep and P < E are shown in Supplementary Figs. 2, 3.