Flood severity along the Usumacinta River, Mexico: identifying the
anthropogenic signature of tropical forest conversion
Abstract
Anthropogenic activities are altering flood frequency-magnitude
distributions along many of the world’s large rivers, yet isolating the
impact of any single factor amongst the multitudes of competing
anthropogenic drivers is a persistent, yet important challenge if we are
to mitigate their negative consequences. The Usumacinta River in
southeastern Mexico provides an ideal opportunity to study an
anthropogenic driver in isolation: tropical forest conversion. This
article employs a novel approach to disentangle the anthropogenic signal
from climate variability, and provides valuable insights into the impact
of forest conversion on flood severity. Here we analyse continuous daily
time series of precipitation, temperature, and discharge to identify
long-term trends, and compare ratios of catchment-wide precipitation
totals to daily discharges in order to account for climatic variability.
We also identify an anthropogenic signature of tropical forest
conversion at the intra-annual scale, successfully reproduce this signal
using a distributed hydrological model (VMOD), and demonstrate that the
continued conversion of tropical forest to agricultural land use will
further exacerbate large-scale flooding. We find statistically
significant increasing trends in annual minimum, mean, and maximum
discharges that are not evident in either precipitation or temperature
records. We also find that mean monthly discharges have increased
between 7% and 75% in the past decade, in contrast to mean monthly
precipitation, which shows no statistically significant trend. Model
results demonstrate that forest cover loss is responsible for raising
the 10-year return peak discharge by 25%, while the total conversion of
forest to agricultural use would result in an additional 18% rise.
These findings highlight the need for a holistic approach to
catchment-wide land management in tropical regions that weights the
benefits of agricultural expansion against the consequences of increased
flood prevalence, and the economic and social costs that they incur.