Step 1: Recall what hydraulic conductivity depends on.
Hydraulic conductivity tells us how easily water moves through soil pores, and it is strongly tied to the viscosity of the water itself.
Step 2: Think about what heat does to viscosity.
Warmer water has weaker internal friction between its molecules, so its viscosity drops as temperature goes up.
Step 3: Connect lower viscosity to easier flow.
Thinner, less viscous water slips through soil pores more easily, so hydraulic conductivity goes up along with temperature.
\[ \boxed{\text{Increase}} \]