Answer:
High heat capacity of the ocean (water body) in coastal areas than that of sand (land) in deserts.
Step-by-step explanation:
The coastal areas have water body (ocean) and the desert are devoid of water bodies. This basic difference in the geography of the two native places makes the entire difference in their temperature at day and night time.
The heat capacity of water is much higher than that of the sand in the desert and due to this reason the time taken by the ocean/sea to heat and to cool is much higher than that of desert.
Therefore, though the day time temperature in desert is higher than that of coastal area , the night time temperature gets lower than the ocean.