Human alterations of the global floodplains 1992-2019

Abstract

Floodplains provide critical ecosystem services; however, loss of natural floodplain functions caused by human alterations increase flood risks and lead to massive loss of life and property. Despite recent calls for improved floodplain protection and management, a comprehensive, global-scale assessment quantifying human floodplain alterations does not exist. We developed the first publicly available global dataset that quantifies human alterations in 15 million km² floodplains along 520 major river basins during the recent 27 years (1992-2019) at 250-m resolution. To maximize the reuse of our dataset and advance the open science of human floodplain alteration, we developed three web-based programming tools supported with tutorials and step-by-step audiovisual instructions. Our data reveal a significant loss of natural floodplains worldwide with 460,000 km² of new agricultural and 140,000 km² of new developed areas between 1992 and 2019. This dataset offers critical new insights into how floodplains are being destroyed, which will help decision-makers to reinforce strategies to conserve and restore floodplain functions and habitat.

Fig. 1

Human alterations of the global floodplains between 1992 and 2019 across 520 major river basins. Human alteration was defined as changes in floodplain land use (e.g., wetland → agriculture) caused by human disturbances that negatively impact floodplain functions. Plot (a) maps the degree of floodplain alteration as percent of floodplain area (i.e., total area of “negatively impacting” land use change within the floodplain/total floodplain area of the basin × 100), thus allowing a consistent analysis regardless of the differences in basin sizes and floodplain extents therein. Note, the floodplain dataset used in this analysis (GFPLAIN250m) does not cover deserts and ice-covered regions. Hence, places like northern Africa, Persian Gulf, Tibetan plateau, and the region above 60 degrees north latitude are not shown in plot (a). To identify the characteristic pattern of floodplain alterations, plot (b) shows how different alteration types in floodplain land use varied at every 250-m spatial resolution along the latitude, as well as the pattern of inter-class land use transitions at continental scales. Plot (b) is further supported by Supplementary Fig. 1 showing how the floodplain alterations at different continents contribute to the overall global floodplain alterations. Plot (c) are time-series graphs showing the continuous increase in the area (km²) of altered floodplains at continental scales along the 27 years of analysis (1992–2019). Plot (d) compares relative degree of alterations within the floodplain and the remaining part of the landscape that is outside the floodplain (i.e., non-floodplain) respectively for every continent. All corresponding data are available for download via HydroShare platform: 10.4211/hs.cdb5fd97e0644a14b22e58d05299f69b.

Fig. 2

Examples of human alterations of floodplains in two of the world’s major river basins: Amazon in South America and Yangtze in Asia. The corresponding time-series graphs show evidence of underlying human disturbance factors by revealing a nearly reciprocal trend of transitions between two dominant land use classes. Other major river basins of the world, e.g., the Great Lakes Basin in North America, Nile River Basin in Africa, Danube River Basin in Europe, Murray River Basin in Oceania show similar examples (Supplementary Figs. 2-3).

Fig. 3

A schematic showing the data development and validation workflow.

Fig. 4

Consistency between the floodplain alteration dataset and a global human modification dataset. The plot shows a parsimonious statistical measure of consistency at continental scales where each dot represents the human modification value for every 250-m altered floodplain grid-cell, and the box represents corresponding 75th percentile, median, and 25th percentile values across continents. The maps are the qualitative measures of spatial resemblance between the two datasets. Because the human modification dataset is not continuous (developed for specific years, e.g., 1990, 2000, 2010, 2015, and 2017), the data presented here are representative of the conditions in year 2017 (i.e., floodplain alterations in 2017 estimated with respect to 1992 are compared with the human modification dataset of 2017).

Fig. 5

Example demonstrating how the global floodplain alteration dataset can be reused for new applications. The plots graphically compare floodplain alteration rates during the past 27 years (1965–1992; based on a 1-km global land use dataset) and the recent 27 years (1992–2019; based on the 0.25-km output dataset presented here). The change rates (km²/year) were calculated with respect to the corresponding base years 1965 and 1992.