All wooden instruments are sensitive to temperature and humidity because all wood expands as it absorbs moisture (or warms) and contracts as it dries out (or cools). Fortunately, the tolerable short-term range of climate conditions is wide as long as sudden changes are avoided and the long-term conditions are good.
The ideal climate range is between 15-25C (60-77℉) and 45-55% relative humidity. Exposure to conditions outside this range may result in temporary poor playability and/or permanent damage depending on how long and how extreme the fluctuations have been.
Low humidity, resulting in over-drying of the wood, is perhaps the biggest danger as this can happen quite quickly and can result in cracking and/or splitting. Other effects include glue joints that separate or become obvious, finish defects, and fret ends that seem to suddenly protrude from the neck of a guitar or ukulele. A very quick way to damage a wooden instrument is to place it near a radiator, heater, or HVAC vent since the more rapid the drying, the more likely there will be splitting. Instruments with laminated wood are a bit more robust in the face of low humidity but care must still be taken.
Very rapid temperature changes may also cause finish checking and cracks.
High heat, especially when combined with high humidity, may potentially melt and “undo” glue joints, and some glues become brittle at higher temperatures. This may happen on Orff boxes but at particular risk of coming loose are the bridge or neck of a guitar or ukulele. Wooden xylophone bars may warp, and bulging or warping of the soundboard (top) of stringed instruments is common in humid conditions.
The best protection for a smaller instrument is a case. In addition to protecting it from scrapes and dings, it acts as a micro-climate. For example, bringing an instrument indoors from the freezing cold (or from a chilly classroom out into a hot car) can be risky but if the instrument is kept in its case for an hour or so before being opened, it will have time to slowly adjust. In areas of very low humidity, a case allows the effective use of an instrument humidifier pack to maintain the desired 45-55% relative humidity. Naturally, the more padded and sealed the case is, the better it will be at insulating the instrument from rapid changes.
Small hygrometers (aka humidity gauges) that can be kept with the instrument(s) are available to monitor humidity, and many home weather stations also have a humidity readout. Electronic gauges are generally recommended over mechanical devices for long-term accuracy.
Solutions for long-term dry conditions:
Solutions for long-term humid conditions:
With a bit of care, wooden instruments may be played and enjoyed for many seasons, despite the weather!