It might seem obvious that the more water you have available, the less vulnerable you are to drought. Or not so obvious?
Comparing counties over the Ogallala with nearby similar counties, groundwater access increased irrigation intensity and initially reduced the impact of droughts. Over time, land-use adjusted toward water-intensive crops and drought-sensitivity increased; conversely, farmers in water-scarce counties maintained drought-resistant practices that fully mitigated higher drought-sensitivity.
That’s from Hornbeck and Keskin, The Evolving Impact of the Ogallala Aquifer: Agricultural Adaptation to Groundwater and Climate.