Evapotranspiration　links　land　surface　hydrological　processes　with　the　atmosphere　and　has　an　important　influence　on　regional　water　cycles　and　the　water　balance.　Research　has　shown　that　urbanization　can　impact　the　hydrological　balance,　leading　to　urban　wet　and　dry　island　effects;　however,　the　mechanisms　driving　these　phenomena　remain　uncertain.　In　this　study,　the　humidity　levels　of　urban　areas　in　China　were　compared　with　the　surrounding　areas　prior　to　(1960-1969),　and　following　(2010-2019)　rapid　urbanization　to　determine　the　drivers　and　mechanisms　of　urban　wet　and　dry　island　effects.　Monthly　observational　datasets　of　temperature,　water　vapor　pressure,　and　relative　humidity　from　613　meteorological　stations　were　combined　with　the　processes　of　urban　artificial　water　dissipation　to　analyze　the　temporal　and　spatial　characteristics　of　urban　dry/wet　islands.　Results　showed　that　cold　and　dry　urban　areas　tended　to　have　wet　island　effects,　while　warm　and　humid　urban　areas　had　dry　island　effects.　The　dry/wet　island　intensity　was　less　than　3.5%　in　most　cities.　Furthermore,　urban　areas　tended　to　be　dry　islands　during　summer　and　wet　islands　during　winter.　Coastal　cities　were　an　exception,　being　dry　islands　throughout　the　year.　Comparisons　of　humidity　prior　to　and　following　rapid　urbanization　revealed　that　absolute　humidity　had　generally　increased,　during　winter,　all　regions　displayed　increased　absolute　humidity,　by　as　much　as　8%-16%　in　northern　China.　This　was　despite　an　overall　trend　towards　increased　dry　island　intensity,　and　was　attributed　to　intensifying　urban　heat　island　effects.　These　results　provide　valuable　information　to　help　understand　the　causes　of　dry/wet　island　effects　in　urban　areas.