(Rhizophora mucronata); and Nonou, (Morinda citrifolia). Scent: Fetau, (Calophyllum inophyllum); Jiali, (Gardenia taitensis); and Boua (Guettarda speciosa); Valla valla, (Premna tahitensis); and Crinum. Medicinal: Tulla tulla, (Triumfetta procumbens); Nonou, (Morinda citrifolia); Tausoun, (Heliotropium foertherianum); Valla valla, (Premna tahitensis); Talla talla gemoa (Psilotum triquetrum); Lou, (Cardamine sarmentosa); and Lakoumonong, (Wedelia strigulosa). Thaman (1992) provides a literature review of the ethnobiology of the Pacific Islands. Climate and natural hazards El Niño and La Niña Tuvalu experiences the effects of El Niño and La Niña that flow from changes in ocean temperatures in equatorial and central Pacific. El Niño effects increase the chances of tropical storms and cyclones; while La Niña effects increase the chances of drought conditions in Tuvalu. On 3 October 2011, drought conditions resulted in a state of emergency being declared as water reserves ran low. Typically the islands of Tuvalu receive between 200mm to 400mm of rainfall per month, however a weak La Niña effect causes a drought by cooling the surface of the sea around Tuvalu. Tropical cyclones Severe tropical cyclones are usually rare, but the low level of islands makes them very sensitive to sea-level rise. Tuvalu experienced an average of three cyclones per decade between the 1940s and 1970s, however eight occurred in the 1980s. The impact of individual cyclones is subject to variables including the force of the winds and also whether a cyclone coincides with high tides. A warning system, which uses the Iridium satellite network, was introduced in 2016 in order to allow outlying islands to be better prepare for natural disasters. George Westbrook recorded a cyclone that struck Funafuti on 23–24 December 1883. A cyclone struck Nukulaelae on 17–18 March 1886. Captain Davis of HMS Royalist, who visited the Ellice Group in 1892, recorded in the ship's diary that in February 1891 the Ellice Group was devastated by a severe cyclone. A cyclone caused severe damage to the islands in 1894. Cyclone Bebe caused severe damage to Funafuti during the 1972–73 South Pacific cyclone season. Funafuti's Tepuka Vili Vili islet was devastated by Cyclone Meli in 1979, with all its vegetation and most of its sand swept away during the cyclone. Cyclone Gavin was first identified during 2 March 1997, and was the first of three tropical cyclones to affect Tuvalu during the 1996–97 cyclone season with Cyclones Hina and Keli following later in the season. Cyclone Ofa had a major impact