Climate change is already putting a strain on international relations and threatening livelihoods.
Mexican farmers are now in the firing line, refusing to end their occupation of La Boquilla Dam.
Mexico is obliged to send 1,750,000 acre-feet of water to the US over a five-year period.
But a lack of rain has left Mexican farmers struggling.
They say sending the water north now would destroy their businesses.
So what happens next?
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