Land　use　change　and　human　activities　associated　with　urbanization　considerably　influence　on　urban　climate.　Many　prior　studies　have　focused　on　rain　and　heat　island　effects;　however,　the　mechanisms　causing　urban　dry　(wet)　islands-characterized　by　lower　(higher)　relative　humidity　in　urban　areas　compared　to　that　in　surrounding　suburbs-have　received　limited　attention.　This　study　coupled　an　artificial　water　dissipation　urban　canopy　model　with　the　Weather　Research　and　Forecasting　model　to　simulate　seasonal　dry　and　wet　island　effects　in　the　Pearl　River　Delta　urban　agglomeration.　Simulations　were　verified　using　observational　datasets　from　representative　urban　and　suburban　meteorological　stations.　Results　showed　that　the　Pearl　River　Delta　urban　agglomeration　tended　to　be　a　dry　island　during　summer,　with　relative　humidity　approximately　4%　lower　compared　to　that　of　the　surrounding　suburbs.　During　winter,　the　dry　island　effect　was　less　apparent　and　showed　more　spatial　variability.　With　the　exception　of　the　northeastern　suburbs,　urban　areas　tended　to　be　drier　(a　relative　humidity　difference　of　approximately　8%)　in　winter.　The　spatial　variability　of　dry　island　effects　during　winter　could　be　explained　by　the　interaction　of　artificial　water　dissipation　and　strong　urban　heat　island　effects.　Artificial　water　dissipation　tended　to　increase　the　relative　humidity　in　urban　areas,　while　heat　island　effects　tended　to　decrease　relative　humidity.　Simulations　were　consistent　with　observations,　including　those　of　dry/wet　islands.　These　findings　highlight　the　role　of　artificial　water　dissipation　in　urban　dry/wet　island　effects　and　illustrate　the　importance　of　considering　artificial　water　dissipation　in　simulations　of　urban　climate.