Two mechanisms behind the drying of the Pantanal: less water arriving

Abstract The Pantanal floods every year, and the system is built on that. We asked whether its recent drying is unusual among the world’s large floodplains and what is driving it. Annual inundated area was extracted for 22 floodplain systems from the JRC Global Surface Water dataset over 1985–2021. Landsat coverage improved across those years, and in fifteen systems the apparent trend still tracked coverage after detrending, so we set those aside as uninterpretable. The Pantanal was not one of them ( rho = − 0.186, p = 0.27) and was the only system with a significant decline (Mann-Kendall τ = −0.402, p < 0.001). Mean inundated area fell from 10,644 km² in 1985–1992 to 6,585 km² in 1993–2021. We compared the satellite record with two Paraguai River gauges, Ladario (since 1900) and Caceres (since 1965). The two agree closely at the expected lag, and satellite coverage adds nothing once river stage is in the model. At Caceres, where water enters the floodplain, flood peaks barely changed (− 6.1%), while dry-season lows nearly halved (− 47.8%, τ = −0.817, p < 0.001), indicating the catchment is holding less water between rains rather than receiving less rain. Flood duration fell 42% at both gauges. Separately, a given river stage now inundates less ground: roughly 2,300 km² less at Ladario and 2,900 km² less at Caceres than before 1993, entirely in seasonal waters. The Pantanal is losing water twice, calling for different responses in different places.