Seasonal and spatial variability in δ18O and δD values in waters of the Godavari River basin: Insights into hydrological processes

Study region: The Godavari River is the largest non-Himalayan, monsoon-fed river in India, providing water resources for ∼75 million people. Study focus: Stable isotopes of Godavari River water in a pre-monsoon (dry) and monsoon (wet) season are used to evaluate seasonal and spatial dynamics and gain insights into hydrological processes, provenance and pathways of river water from source to sea. New hydrological insights: Godavari River water isotopes shift from an evaporation- to precipitation-controlled signature between the pre-monsoon and monsoon season (p ≤ 0.001). Godavari waters plot below Global and Local Meteoric Water Lines (p ≤ 0.01), highlighting the importance of evaporation. In the monsoon season, low δ18O and δD values in the downstream catchment reflect an amount/convective effect caused by Southwest monsoonal rainfall. Continuously enriched signatures in the Upper Godavari suggest year-round evaporation due to a rainfall deficit and abundant dams creating stagnant waters. The Godavari ultimately discharges an integrated, monsoon signal into the Bay of Bengal. River depth profiles reveal that Godavari waters are well-mixed in both seasons. In the pre-monsoon season, Godavari water isotopes suggest basin-wide evaporation and seawater intrusion in the delta. A data compilation (n = 399) of δ18O and δD values in Indian Rivers reveals a strong seasonality for the Godavari River. The spatio-temporal patterns in Godavari River water isotopes confirm their suitability as sensitive recorders of monsoon precipitation variability and hydrological processes within monsoon-fed rivers