I tried uploading picture of the same but looks like some error.
Terrace gardens imply a hard surface attached to a building such as a balcony where the raised area overlooks something visually appealing and the garden consists of plants in planters and other boxes and pots massed together.
An example of a terrace garden from Wikipedia (https://commons.wikimedia.org/wiki/File:Terrace_Garden_East-57th-St_New_York.jpg)
The big issue is that in contrast to an open garden the plants are confined to a smaller volume for the roots to grow in. This requires close attention to irrigation and feeding of the plants to ensure their continued health.
Hibiscus provide showy flowers but they are vigorous shrubs which will quickly fill a planter or pot. In addition if the planters lack free drainage the roots will suffer with rot if given too much water.
The drying indicates that something has gone wrong with the roots. Either they have filled the container and exhausted all the nourishment in that soil, or there is something wrong with the quality of the water used for irrigation; perhaps too much salt has built up, or overwatering has deprived the roots of air.
Since several plants are showing distress all at the same time you might give serious consideration to the plants having filled their growing place and are in need of replacement.
If it's been in the same pot for 4 years, it may well need potting on into something larger by now. Turn it out of its pot to check and if you see roots coiling round and round, it needs a larger container. When a plant runs out of sufficient root room, it starts to drop lower leaves, though growth at the top may continue; its also difficult for the plant to get sufficient water because the ratio of root to soil in the pot is wrong.
The soil in the pot looks as if its been disturbed; it's not evenly distributed and looks a bit lumpy, so have you been digging around in it for some reason? If you do repot, use new potting soil.
Otherwise, closely inspect the whole plant from top to bottom, including backs of leaves, to make sure there is no other problem with spider mites, insect infestation or disease.