( ( ( ( ( Thus ( ( ( water levels ) ( in reservoirs ) ) decline ) ) , ) and ) ( ( water problems ) ( develop ( during ( these ( long ( dry periods ) ) ) ) ) ) ) . )
(ROOT (S (S (ADVP (RB Thus)) (NP (NP (NN water) (NNS levels)) (PP (IN in) (NP (NNS reservoirs)))) (VP (VBP decline))) (, ,) (CC and) (S (NP (NN water) (NNS problems)) (VP (VBP develop) (PP (IN during) (NP (DT these) (JJ long) (JJ dry) (NNS periods))))) (. .)))
Thus water levels in reservoirs decline, and water problems develop during these long dry periods.
(ROOT (S (NP (DT A) (NN reservoir)) (VP (VBZ is) (NP (NP (NN part)) (PP (IN of) (NP (NP (DT a) (NN cycle)) (SBAR (WHNP (WDT that)) (S (VP (VBZ holds) (NP (NP (DT an) (NN element) (CC or) (NN water)) (PP (IN for) (NP (NP (DT a) (JJ long) (NN period)) (PP (IN of) (NP (NN time))))))))))))) (. .)))