Deciphering the relationship between meteorological and hydrological drought in Ben Tre province, Vietnam

The low-lying Vietnamese Mekong Delta (VMD) is a key agricultural production landscape
increasingly threatened by anthropogenic stresses and climate change. Among the different
threats, droughts caused by extreme events, climate change and upstream developments,
affect the delta the most. This paper explores the relationship between the intensity, duration,
and frequency of meteorological droughts and hydrological droughts using a range of
indices. We used monthly rainfall and stream flow data for the period 1992–2021 to calculate
the Standardized Precipitation Index (SPI), the Reconnaissance Drought Index (RDI),
and the streamflow drought Index (SDI) for different time intervals. We found no observed
time lag, and a strong correlation coefficient between upstream hydrological and downstream
meteorological drought events assessed over long-term scales (i.e., 12-months).
This is true for all downstream sites, except Ben Tre City. Hydrological drought events
onset lagged 5–6-, 6-, and 3–4-month behind meteorological droughts at mid- and shorter
assessment time scales (9-, 6-, 3-month). The average correlation coefficients between
hydrological indices and meteorological indices at 9–3-month time scales ranged from
moderate to weak. These findings shed light and advance the understanding of the progression
of meteorological to hydrological droughts in the VMD. Our results aid the regional
understanding of drought onset and the causative mechanisms at work, which is important
for both medium- and long-term drought forecasting and adaptation planning.