Disentangling the relative impacts of precipitation reduction and vapour pressure deficit (<
i>
VPD<
/i>
) on plant water dynamics and determining whether acclimation may influence these patterns in the future is an important challenge. Here, we report sap flux density (<
i>
F<
sub>
D<
/sub>
<
/i>
), stomatal conductance (<
i>
G<
sub>
s<
/sub>
<
/i>
), hydraulic conductivity (<
i>
K<
sub>
L<
/sub>
<
/i>
) and xylem anatomy in pi�on pine (<
i>
Pinus edulis<
/i>
) and juniper (<
i>
Juniperus monosperma<
/i>
) trees subjected to five years of precipitation reduction, atmospheric warming (elevated <
i>
VPD<
/i>
) and their combined effects. No acclimation occurred under precipitation reduction: lower <
i>
G<
sub>
s<
/sub>
<
/i>
and <
i>
F<
sub>
D<
/sub>
<
/i>
were found for both species compared to ambient conditions. Warming reduced the sensibility of stomata to <
i>
VPD<
/i>
for both species but resulted in the maintenance of <
i>
G<
sub>
s<
/sub>
<
/i>
and <
i>
F<
sub>
D<
/sub>
<
/i>
to ambient levels only for pi�on. For juniper, reduced soil moisture under warming negated benefits of stomatal adjustments and resulted in reduced <
i>
F<
sub>
D<
/sub>
<
/i>
, <
i>
G<
sub>
s<
/sub>
<
/i>
and <
i>
K<
sub>
L<
/sub>
<
/i>
. Although reduced stomatal sensitivity to VPD also occurred under combined stresses, reductions in <
i>
G<
sub>
s<
/sub>
<
/i>
, <
i>
F<
sub>
D<
/sub>
<
/i>
and <
i>
K<
sub>
L<
/sub>
<
/i>
took place to similar levels as under single stresses for both species. Here our results show that stomatal conductance adjustments to high <
i>
VPD<
/i>
could minimize but not entirely prevent additive effects of warming and drying on water use and carbon acquisition of trees in semi-arid regions.