Hydrological conditions that directly impact terrestrial wildlife and people in and around Bardia National Park (Nepal)

It is increasingly realised that hydrological conditions are not only an abiotic factor for plant communities but also for animals on land including megafauna. Acknowledging the hydrological conditions is of major importance as anthropogenic activities as well as natural processes may change these conditions. Here, we investigate the hydrological conditions and their changes that directly affect terrestrial wildlife in Bardia National Park and the people that live adjacent to this nature reserve. Bardia NP is situated in the flat Terai Arc Landscape at the foot of the Himalayas and hosts the One-Horned Rhinoceros, the Bengal Tiger and the Asian Elephant amongst others.Bardia NP is bordered in the west by the Geruwa branch of the Karnali River, which is draining the Himalayas in Western Nepal and one of the major tributaries of the Ganges River. Extensive floodplains are associated with the Geruwa branch. High densities of rhinoceros and tigers have been found here thanks to the existing natural water pools as drinking water and cooling facility, dense grassland-forest mosaics providing forage for the rhinoceros and the deer (being prey for the tigers) and also shelter for the tigers. Flow in the Geruwa branch has gradually declined since the intense, double-peaked 2009 Monsoon, which deposited very coarse sediment (boulders) over the Geruwa’s upstream end, contributing to the gradually reducing flow since. The Geruwa branch has been drying up since that time. This has two major implications for wildlife and also human-wildlife conflicts. First, about half of the rhinoceros population has moved to the Indian nature reserve further south in recent years assumed to do so in search for water pools. Second, the Geruwa branch has become a less vivid river for which it is easier for wildlife to cross during wet periods. Strikingly, this area has also been most vulnerable for human – wildlife conflicts in recent years (Paudel et al., 2024, Ecology and Evolution, 2024; 14:e70395).Another hydrological condition is posed by the artificial water holes at Bardia NP. There are c. 180 artificial water holes around the natore reserve that are essential for drinking water to wildlife. Not all of them are permanent and several rely on groundwater pumping using solar energy. The migration behaviour of the tigers is influenced by their presence as indicated by agent-based modelling of tiger behaviour, and supported by field observations (Thapa et al., Species 2023; 24: e91s1619).Finally, small irrigation canals are present in the rural area between Bardia NP and the Nepalese – Indian border. It is currently hypothesized that maintenance activities to reduce leakage of these canals have also diminished groundwater recharge. Upon consequence, the groundwater table may have dropped along these canals to depths that are outside the pumping range of hand pumps. These hand pumps are the main drinking water supply for the local communities and the impression is that there is an increasing trend for hand pumps to run dry. This should be further investigated by interviews and hydrological monitoring.