Having lived in California, so much of their rain water actually just runs down the sewers. It’s so hard for the water to absorb into their soil because it’s become just baked into almost a crust. Having green space will probably make it easier for water to penetrate into the soil and be retained in the soil.
The fumes from lithium ion are much more harmful. They can affect people just in the vicinity. And not in some worst case scenario of gas somehow spreading to occupants of the vehicle.
Gas tanks are generally very well confined. And if one were to rupture. It is likely to spread to the ground, not spray some imaginary people.